Diet format, protein, amino acids, salt, and osmolytes, as well as water viscosity, affect water consumption in domestic cats: a scoping review of 32 publications (published from 1975 to 2025) on water intake, hydration status, and related health outcomes

Abstract

Ensuring cats consume sufficient water to maintain their health is a common concern for cat owners. Despite the connection between water intake and animal health, the optimal water intake levels for cats are poorly understood. The present scoping review aimed to determine the extent to which cat hydration research has been conducted, the reported average daily water intake of cats, and whether their water intake requirements have been identified. Online databases were used to identify papers published between 1975 and 2025, from which we selected 32 publications written in English that provided the water intake of cats as an outcome variable. Across an assessment of five groups of healthy domestic cats, 23 to 51 mL/kg BW of total water was consumed daily. A further eight papers reported that cats consumed 70 to 293 mL of water daily. Urine specific gravity (USG) was the most reported physiological biomarker used to assess a cat’s hydration status and is used to assist in the diagnosis of diabetes insipidus, glomerulonephritis, pyelonephritis, adrenal insufficiency, hepatic disease, and congestive heart failure. USG was frequently measured in conjunction with urine pH, volume (or output), calcium oxalate, struvite, and/or serum biochemistry and a complete blood count to evaluate gross kidney function. The water intake of cats was highly variable within and across studies. Still, it was influenced by factors such as diet format (wet or dry), dietary protein or amino acid content, salt, osmolytes, and water viscosity. The water intake of cats was not affected by fat content or water source type (static or flowing). Healthy cats that consumed 42 to 51 mL/kg BW of total water daily often had a USG <1.035, and this was achieved only when consuming a wet diet or a dry diet with supplemented nutrient-enriched water. Except for those supplemented with nutrient-enriched water, cats on a dry diet had lower TWI and higher USG, suggesting they may be at greater risk of developing feline lower urinary disease, including crystalluria and urolithiasis. Although the minimum water requirement before cats become at a greater risk of developing urinary or renal disease remains unknown, these results provide some evidence of the minimum water intake required for optimal hydration. If not consumed, these cats would likely benefit from a wet, semi-moist, or fresh (high-moisture) diet.

The water intake of cats is influenced by the composition and format of their diet, as well as by the viscosity of the water. Healthy cats consume 23 to 51 mL/kg of water daily; however, cats at a high risk of feline lower urinary disease may benefit from consuming 42 to 51 mL/kg BW of water daily.

Introduction

Maintaining hydration is essential for the health of all animals. Sudden or significant changes in body water content can result in altered perfusion of organs and tissues. In humans, the total water intake (TWI) is a minimum of 1.8 L/d to avoid dysregulation of metabolic function and subsequently prevent renal or urinary disease, as identified through the assessment of plasma arginine vasopressin (AVP) concentration (Armstrong and Johnson, 2018). It is estimated that domestic cats do not consume enough water; however, their water requirement has not been empirically determined. The natural diet of cats typically consists of whole prey, with free-roaming feral cats primarily consuming rats, mice, voles, rabbits, and other small mammals (Plantinga et al., 2011). These prey items contain approximately 65% to 75% moisture (Bird et al., 1982; Powers et al., 1989; Clum et al., 1996; Clum et al., 1997), whereas dry, shelf-stable, commercial diets contain approximately 3% to 11% moisture. Given that 16%–40% of cat owners feed a commercial dry diet (Laflamme et al., 2008; O’Halloran et al., 2024; Hunter and Murison, 2025), cats may require more free water from external sources. Despite this, it is often reported that cats are inefficient at drinking due to physiological and behavioral factors. Since cats cannot rely on suction, like humans, or scooping water with their tongues, like dogs, they lap water into their mouths to drink, which involves pressing their tongue on the water’s surface and lifting it into their mouths rapidly. Cats lap an average of 3.5 times per second, with an average of 0.14 mL per lap (Reis et al., 2010), compared to dogs, which lap on average 4 times per second and can scoop ∼2.5 mL of water per lap, depending on size and breed (Gart et al., 2015). According to the NRC, cats should consume 50 to 60 mL/kg body weight (BW) of water (NRC, 2006). However, this estimate is based on the water intake requirement of dogs (Schaer, 1989) and does not account for differences in diet composition, dry matter intake, environmental temperature, or activity level. This said, using this formula, the average 4 kg cat would need to consume up to 200–240 mL of water per day, completing 1,429 to 1,714 laps for a total of 6.8 to 8.2 min, based on the example calculation below:

$$\begin{array}{l}\left(\text{4\hspace{0.17em}kg BW }\times \text{ 5}0\text{\hspace{0.17em}mL of water}\right)/\left(0.\text{14\hspace{0.17em}mL per lap}\right)=\text{ 1},\text{429 laps}\\ \left(\text{1},\text{429 laps}/\text{3}.\text{5 laps}/\text{s}\right)/\text{6}0\text{\hspace{0.17em}s per min\hspace{0.17em}}=\text{\hspace{0.17em}6}.\text{8\hspace{0.17em}min}\end{array}$$

Ensuring cats consume enough water to maintain their health is a common concern for cat owners. Renal disease, cystitis, and feline urologic syndrome were reported in approximately 2%, 2%, and 1.5% of cats, respectively, from 52 veterinary practices (n = 15,226 medical records) (Lund et al., 1999), with renal disorders as one of the leading causes of death in cats, reported by a primary veterinary practice in England (O’Neill et al., 2015). In addition, chronic kidney disease (CKD) is estimated to affect 1–3% of the general cat population (Grauer et al., 2017). However, a greater frequency has been reported in cats admitted to veterinary clinics. For example, CKD was present in 50% of cats randomly selected from a veterinary clinic in North Carolina, with a greater prevalence in geriatric cats aged 15–20 (81%) than in young or adult cats aged 0–4.9 (37.5%), 5–9.9 (41%), and 10–14.9 (42%) (n = 86 medical records) (Marino et al., 2014).

Importantly, urinary or renal diseases are commonly associated with water consumption behavior, either as a risk factor or clinical signalment. Cats were more likely to be diagnosed with CKD if their owners observed polydipsia (excessive thirst) or polyuria (frequent urination) within the year (Bartlett et al., 2010). Further, dehydration is exacerbated in cats with CKD given their inability to consume enough water to compensate for frequent urination (Greene et al., 2014). While the direct connection between water intake and renal function in cats is unclear, this relationship has been established in humans. In a study of 1,265 patients with CKD, those who drank <0.5, 0.5–1.0, 1.5–2.0, or >2.0 L of water per day were at a greater risk of renal failure than those who drank 1.0–1.5 L/d (Wagner et al., 2022). Therefore, both under- and overconsumption of water are associated with poor renal function in humans with CKD. In addition, research in humans has reported that even mild or short-term dehydration can lead to the onset or progression of type two diabetes (Johnson et al., 2017; Choi et al., 2025), fatigue, poor concentration, headaches in women (Armstrong et al., 2012), and reduced cognition (Armstrong et al., 2012), as well as an increased risk of constipation (Klauser et al., 1990) in men. Without a clear understanding of normal drinking patterns in cats, it is difficult to identify individuals at risk of chronic dehydration and its consequences, or to implement early interventions that may slow CKD progression.

The causes of urinary and renal disease are multifactorial, with hydration playing an important role. Not drinking enough water can lead to underhydration or dehydration, resulting in more concentrated urine (Popowski et al., 2001; Logan-Sprenger and Spriet, 2013). While individual variation limits the ability to use urinary measures for the determination of intracellular dehydration, urine specific gravity (USG), can be used as a valuable marker for dynamic dehydration assessments (Cheuvront et al., 2010) and to help detect possible abnormalities in the AVP hormone (Nollen et al., 2025). In healthy cats, USG ranges from 1.020 to 1.051, depending on their age, diet, and fasted/fed state (Rishniw and Bicalho, 2015; Rudinsky et al., 2024). However, a large-scale study reported that 87.6% (855/976) of apparently healthy cats over 6 mo old had a USG above 1.035 (data submitted by 128 different clinicians; Rishniw and Bicalho, 2015). While cats can concentrate their urine more effectively than most other mammals (Chew, 1965), a low water intake and a high USG can also indicate dehydration. Conversely, the onset of a low USG might suggest poor concentration ability and renal disease. Cats admitted to a veterinary clinic with compensated (n = 9), uremic (n = 30), and end-stage (n = 13) renal failure had an average USG of 1.025, 1.018, and 1.014, compared to 1.038 in healthy cats (Elliott and Barber, 1998). TWI (water and food moisture), diet composition, age, and environmental factors should all be considered when interpreting USG and assessing the risk of renal and urinary disease.

While the connection between chronic dehydration and the health status of domestic cats is well documented, the volume of water required for optimal hydration and to reduce disease risk has not been thoroughly investigated. Defining sufficient water intake for cats to be optimally hydrated is needed before developing subsequent strategies to improve hydration status. Therefore, the objectives of this scoping review are to determine the extent of research on cat hydration, the water intake requirements of healthy cats, and their reported average water intake (with or without dietary intervention).

Materials and Methods

This review was conducted following the PRISMA-Scr (Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews) guidelines (Tricco et al., 2018). The research questions are: (1) To what extent has cat hydration research been conducted? (2) What is the average daily water intake of cats? (3) Has the daily water requirement for cats been identified?

Information sources

This review encompasses studies from peer-reviewed primary research and pilot studies published since 1975, written in the English language. From April to May 2025 (with the last search conducted on May 29, 2025), searches were conducted in peer-reviewed research databases. Tailored search strategies were performed across Google Scholar, Ovid Medline, PubMed, and Web of Science. Search terms included (“cat” OR “cats” OR “feline” OR “felines”) AND (“hydration” OR “water intake”). Search strings were optimized to produce the greatest number of relevant results. Boolean operators were used according to each database’s allowed strategy. Files were downloaded in RIS (Google Scholar, OVID Medline, and Web of Science) or PubMed format and uploaded to Covidence.

Eligibility criteria

In the first stage of eligibility screening, two team members (PALK and GG) independently assessed the titles and abstracts of each search result based on the inclusion and exclusion criteria, as follows: research articles must have been written in English from 1975 to 2025 and focus on cat hydration. Data on the daily water intake of cats must have been presented in the text in numerical format. Studies assessing water intake in cats with renal or urinary disease were within the scope. These criteria ensure the inclusion of diverse and relevant research on the topic. Secondary evidence, such as review articles, was excluded to avoid redundancy and maintain the review’s scope. Studies that did not present water intake or were conducted in animals other than cats were excluded. All articles selected as “yes” or “maybe” by either reviewer were put forward for full-text review at this stage; articles where both reviewers selected “no” were excluded. Inclusion decisions were compared, and disagreements were resolved through verbal consultation. The search and study selection processes were documented in a PRISMA flow diagram. The proportionate agreement was reported through Covidence as 0.833, representing near-perfect inter-rater reliability (Watson and Petrie, 2010).

Data extraction

One research team member (PALK) extracted and recorded the relevant data. Extracted data included the study population, sample size, study design, duration, and location, as well as diets and/or treatments, water intake, measures of hydration status, and the effects of diet or supplements on hydration status. A figure was created to represent the relationship between water intake and USG after data extraction. For this, the average daily TWI for each treatment group, as well as the urine specific gravity at the end of each phase, were recorded (Supplementary Table 1). Following this, TWI and USG were grouped into categories and the number of studies in each category was counted.

Results

A total of 1,126 records were screened for eligibility, and 876 relevant titles and abstracts were identified for potential inclusion after removing duplicates (n = 249). Fifty-two texts were identified for full screening; however, four full texts could not be retrieved for review. Of the 48 full texts screened, ten were excluded due to study outcomes (four of which noted a difference in water intake between treatment groups; however, water consumption data were not provided in the text), and six were excluded due to the study design. Thirty-two relevant texts were identified (Figure 1). Studies used a sample size of 2 to 55 cats. The majority (26/32; 81%) of studies were conducted in laboratory settings and employed a crossover (CO) design (12/32; 37.5%) (Table 1).

Figure 1.

Prisma flow diagram of included studies on water intake of cats.

Table 1.

An overview on the effects of dietary and water treatment on water intake and hydration status in cats

Sample population	Diets and treatments provided	Study design and duration	Study environment	Water consumption*	Hydration status	Treatment effects on hydration	Source
Healthy cats (n = 8; 4 females and 4 males)	(1) High fibre round shape dry (8.5% moisture) (2) Low fibre round shape dry (8.5% moisture) (3) High fibre triangular shape dry (8.5% moisture) (4) Low-fibre triangular shape (8.5% moisture)	CO; 7d/leg	Laboratory—Unsp.	FWI: 54 mL/d	NP	NP	Armbrust et al. (2003)
Healthy mixed breed cats (n = 17; 6 females and 11 males)	(1) Dry + 0.6 % KCl (7.8% moisture) (2) Dry + 1.9% KCl (7.7% moisture)	CO; 10d/leg	Laboratory—group cat colony; individual cages during collection period	FWI: 28.5 mL/kg/d—33.8 mL/kg/d	USG: 1.058–1.069 pH: 5.93 UE: 11.2–16.2 mL/kg/d CaOx RSS: 2.59–3.24 Oxalate: 1.48–1.63 mmol/L Uric acid: 0.6–0.8 mmol/L MAP RSS: 0.17–0.29	Cats on the high KCl diet had ↑ FWI, ↑ UE, ↓ USG, ↓ CaOx RSS, ↓ oxalate, and ↓ uric acid	Bijsmans et al. (2021)
Healthy DSH cats (n = 8; 2 females; 6 males)	(1) Home-cooked (65% moisture) (2) Canned urolithiasis (81.1% moisture) (3) Dry urolithiasis + high sodium (4.2% moisture) (4) Dry (5.1% moisture) (5) Dry (5.1% moisture) + zucchini	LS; 21d/leg	Laboratory—group cat colony during adaptation; individual during collection period	TWI: 27–42 mL/kg/d	USG: 1.031–1.065 pH: 6.3–7.4 UE: 11–25 mL/kg/d CaOx RSS: 1.1–5.7 FWE: 1–5 mL/kg/d	Cats on a wet diet had the greatest ↑ TWI, ↑ UE, and ↓ USG	Blanchard et al. (2022)
Healthy cats (n = 6; 3 females and 3 males)	(1) Dry (6.3% moisture) (2) Dry + water (25.4% moisture) (3) Dry + water (53.2% moisture) (4) Dry + water (73.3% moisture)	RBD; 21d	Unsp.	TWI: 98.6–144.7 mL/d	USG: 1.054–1.036 pH: 6.19–6.23 UE: 86.7 mL/d for 73.3% moisture group CaOx RSS: 1.14–2.295	Cats on the 73.3% moisture diet had ↑ TWI, ↑ UE, ↓ FWI, ↓ USG, and ↓ CaOx RSS	Buckley et al. (2011)
Healthy cats (n = 28 females)	(1) Dry low fiber (8.0% moisture) (2) Dry + cellulose (6.5% moisture) (3) Dry + beet pulp (7.6% moisture) (4) Dry + pectin/arabic gum (7.5% moisture)	RBD; 15d	Laboratory—group housing (2–3 cats/group)	FWI: 127.3–226.4 mL/d	pH: 7.20–7.28 Urine mOsm/kg: 250–298	Cats on the cellulose diet had ↑ FWI and ↑ pH, whereas cats on the pectin/arabic gum diet had ↓ FWI Cats on the low fibre diet had ↑ mOsm/kg, whereas cats on the beet pulp diet had ↓ mOsm/kg	Bueno et al. (2000)
Healthy cats (n = 10 females)	(1) Moderate fat and protein dry (% moisture unsp.) (2) Moderate fat and protein dry + 50.0% water (3) High fat and protein dry (% moisture unsp.) (4) Wet (% moisture unsp.)	LS; 10d/leg	Laboratory –individual metabolic cages	TWI: 105.6–158.0 mL/d FWI: 16.8–93.5 mL/d MW: 15.6–20.2 mL/d	TWE: 47.0–91.1 mL/d FWE: 9.7–34.7 mL/d UE: 20.6–68.5 mL/d IL: 58.1–67.6 mL/d	Cats on the wet diet had ↑ TWI, ↑ UE, ↑ TWE, and ↓ FWI	Carciofi et al. (2005)
Healthy European shorthair cats (n = 13; 6 females and 7 males)	(1) Home-cooked (% moisture unsp.) (2) Home-cooked + high phosphorus (% moisture unsp.)	Parallel; 29d	Laboratory—group cat colony	TWI: 29.8–34.8 g/kg/d	USG: 1.046–1.062 UE: 13.9–15.4 g/kg/d FWE: 2.5–2.8 g/kg/d IL: 13.4–16.6 g/kg/d	Cats on a high phosphorus had ↑ TWI, ↑ IL, ↑ USG, ↑ renal P excretion, and 9/13 had glucosuria and microalbuminuria.	Dobenecker et al. (2018)
Adult healthy cats (n = 6; 3 females and 3 males)	(1) Dry with fish meal (% moisture unsp.) (2) Dry with CGM (% moisture unsp.)	CO; 21d/leg	Laboratory—individual metabolic cages	FWI: 39.2–50.2 mL/kg/d	UE: 21.8–25.6 mL/kg/d pH: 6.25–6.33 Urea: 26.8–40.2 g/kg/d Fecal moisture: 63.7–73.0%	Cats on a fish meal diet had ↑ fecal moisture content and ↓ urea.	Funaba et al. (2001)
Healthy cats (n = 24 females)	(1) Dry 28.0% CP + 0.58% sodium (6.4% moisture) (2) Dry 39.0% CP + 0.64% sodium (4.8% moisture) (3) Dry 52.0% CP + 0.76% sodium (5.3% moisture) (4) Dry 64.0% CP + 0.87% sodium (5.3% moisture)	RCBD; 51d	Laboratory—individual experimental cages	TWI: 81.5–105.2 mL/d MW: 16.9–18.2 mL/d	USG: 1.051–1.059 pH: 6.57–7.16 E: 34.1–60.1 mL/d FWE: 7.5–12.8 mL/d IL: 34.6–36.0 mL/d Renal urea excretion: 2.46–6.28 g/d	Cats on a high protein and high sodium diet had ↑ FWI, ↑ TWI, ↑ pH, ↑ renal urea excretion, ↑ fecal score, ↑ UE, and ↓ feces (g/cat).	Garcia et al. (2021)
Healthy cats (n = 20; 5 females and 15 males	(1) Dry (5.7% moisture) (2) Wet (75% moisture)	CO; 28d	Laboratory—individual experimental cages	FWI: 20–57 mL/d	NP	Cats on a wet diet had ↓ FWI	Goggin et al. (1998)
Healthy mixed breed cats (n = 12; 6 females and 6 males)	(1) Unsp. – water bowl (2) Unsp. – water fountain	CO; 14d/leg	Indoor client-owned	FWI: 22.9–33.1 mL/kg/d	USG: 1.044–>1.060 Urine mOsm/L: 1977–3231	None.	Grant (2010)
Healthy cats (n = 12; 7 females and 5 males)	(1) Dry (% moisture unsp.) (2) Dry + 1% methylcellulose in water (% moisture unsp.)	CO; 56d/leg	Laboratory—individual rooms	FWI: 32.5–45.8g/100 kcals/d	USG: 1.046–1.053 pH: 6.14–6.29 Serum mOsm: 320.5–323.0 CaOx RSS: 3.22–3.59 Struvite RSS: 3.90–7.75	Cats provided with 1% methylcellulose in their water had ↑ FWI, ↓ serum creatinine, ↓ urea, cholesterol, ↓ urea triglycerides, ↓ USG, ↓ urine Ca, and ↓ CaOx RSS.	Hall et al. (2021)
Healthy cats (n = 7 females)	(1) Dry 55% CP (8.5% moisture) (2) Dry 29% CP (6.2% moisture)	Parallel; 1 yr	Laboratory—individual metabolic cages	FWI: 92.3–244.6 mL/d	UE: 39.8–112.4 mL/d	Cats on a high protein diet had ↑ TWI and ↑ UE	Hashimoto et al. (1996)
Healthy cats (n = 4 females)	(1) Dry 25.9% CP (% moisture unsp.) (2) Dry 38.3% CP (% moisture unsp.) (3) Dry 51.4% CP (% moisture unsp.) (4) Dry 65.2% CP (% moisture unsp.)	LS; 21d/leg	Laboratory—individual metabolic cages	TWI: 70.0–125.9 mL/d	UE: 38.0–73.7 mL/d	Cats fed a high protein diet had ↑ TWI, ↑ UE, and ↑ P excretion.	Hashimoto et al. (1995)
Healthy cats (n = 55 mixed sex)	(1) 10 dry low sodium (<7.32 g Na/MJ; % moisture unsp.) (2) 13 dry high sodium (11.51–16.74 g Na/MJ; % moisture unsp.)	Parallel; 21d	Laboratory—individual metabolic cages	FWI: 110–141 mL/d	USG: 1.045–1.051 pH: 6.26–6.38 UE: 55–78 mL/d CaOx RSS: 2.49–2.95	Cats fed diets higher in sodium had ↑ FWI, ↑ UE, ↓ USG, and ↓ CaOx RSS.	Hawthorne and Markwell (2004)
Healthy domestic shorthair adult cats (n = 6 males)	(1) Dry (0.8 ppm Se; 10% moisture) (2) Dry (1.125 Se; 10% moisture) (3) Dry + water (0.8 ppm Se; 75% moisture)	LS; 28d/leg	Laboratory—group cat colony	TWI: 120–192 mL/d	NP	Cats on the 75% moisture diet had ↑ FWI	Hooper et al. (2018)
Healthy young cats (n = 2 females)	(1) Ground dry (% moisture unsp.) (2) 80% Ground dry + 20% celluflour (% moisture unsp.)	OCE; 10d or until 6d of consecutive measurements	Laboratory—individual metabolic cages	FWI: 75.2–98.3 mL/d	NP	Cats on a dilute diet had ↑ FWI/kcal food.	Kanarek (1975)
Healthy SPF cats (n = 8; 2 females and 6 males)	(1) Dry 45% fat (% moisture unsp.) (2) Dry 15% fat (% moisture unsp.)	CO; 10d low fat + 21d high fat; PT; 14d	Laboratory—individual metabolic cages	FWI: 99.4–112.8 mL/d Bout volume: 10.2–12.6 mL	NP	None.	Kane et al. (1987)
Healthy adult SPF cats (n = 8; 4 females and 4 males)	(1) Dry (7.7% moisture) (2) Wet (76.6% moisture) (3) Casein-based purified (4.5% moisture) (4) AA-based purified (4.3% moisture)	CO; 7–10d/leg	Laboratory—individual metabolic cages	FWI: 79.4–147.3 mL/d TWI: 1.1–3.5 mL/g DMI	NP	Cats on a wet diet had ↑ TWI and ↓ FWI. Cats on a AA-purified diet had ↑ FWI than the wet diet, but a ↓ FWI than the dry diet.	Kane et al. (1981)
Healthy Chartreux cats (n = 14; 10 females and 4 males)	(1) Dry (4% moisture) (2) Dry +5 × 109 CFU/kg S. cerevisiae (4% moisture)	Parallel; 35d	Client-owned	FWI: 180–210 mL/d	Fecal moisture: 41.2–68.6 %	None.	Lonigro et al. (2025)
Healthy mixed breed cats (n = 24; 14 females and 10 males)	(1) Dry high starch (6.5% moisture) (2) Dry high protein-low hydroxyproline (soy-based) (5.8% moisture) (3) Dry high protein- high hydroxyproline (5.4% moisture)	CRD; 18d	Laboratory—individual experimental cages	TWI: 22.8–34.8 mL/kg/d FWI: 16.8–29.0 mL/kg/d MW: 4.6–5.3 mL/kg/d	USG: 1.062–1.065 pH: 6.57–6.97 UE: 9.2–19.6 mL/kg/d FWE: 3.4–4.0 mL/kg/d IL: 7.3–12.7 mL/kg/d	Cats fed the soy-based diet had ↑ TWI, ↑ FWI, ↑ pH compared to cats fed the high starch diet Cats fed the high starch diet had ↓ UE	Mendonça et al. (2018)
Healthy adult cats (n = 9 unsp. sex)	(1) Dry (% moisture unsp.) + flowing water (2) Dry (% moisture unsp.) + still water	PT; 4d	Shelter—individual rooms	FWI: 109.8–115.4 mL/d	NP	None	Pachel and Neilson (2010)
Clinically dehydrated cats (n = 13; 9 females and 4 males)	(1) Dry (% moisture unsp.) + NW (2) Wet (% moisture unsp.) + NW (3) Mixed (% moisture unsp.) + NW	Clinical; 2d	Client-owned	FWI: post-treatment: 179 mL/d	USG: pre-treatment: 1.018–1.052; post-treatment: 1.018–1.050 Urine mOsm/kg: pre-treatment: 317–336 post-treatment: 316–355 PCV: pre-treatment: 21–43 %; post-treatment: 23–43% Fluid deficit: pre-treatment: 75 mL/kg; post-treatment: 51 mL/kg	Cats showed ↓ in fluid deficit post NW consumption and ↑ hydration scores.	Peralta et al. (2025)
Healthy cats (n = 24; mixed sex)	(1) Dry (31.6% moisture) (2) Dry + 0.3% acidifiers (33.0% moisture) (3) Dry + 0.6% acidifiers (31.4% moisture) (4) Dry + 0.9% acidifiers (31.1% moisture)	CRD; 16d	Laboratory—individual metabolic cages	TWI: 123.6–139.3 mL/d FWI: 117.7–132.7 mL/d	UE: 36.22–51.73 mL/d	None.	Pires et al. (2013)
Healthy adult cats (n = 14; 9 females and 5 males)	(1) Dry (6% moisture) + flowing water (2) Dry (6% moisture) + circulating water (3) Dry (6% moisture) + still water	CO; 14d/leg	Laboratory—group cat colony	FWI: 26.1–27.5 mL/kg/d	USG: 1.050–1.051 UE: 15.0–15.9 mL/kg/d Urine mOsm/L: 2108.6–2584.7 CaOx RSS: 0.31–0.80 Struvite RSS: 2.01–3.27	Cats drinking from a circulating water system had ↑ mOsm. Three individual cats showed a preference one of the bowl types, but there was no significant preference across all groups.	Robbins et al. (2019)
Healthy adult domestic shorthair cats (n = 10; 5 females and 5 males)	(1) Dry (8.8% moisture.) (2) Wet (76.8% moisture)	Single group CO; 14d/leg	Laboratory—individual experimental cages	TWI: 139.0–174.6 mL/d FWI: 22.8–167.2 mL/d	Body water: 58.1–50.2% Body water turnover: 151.7–182.3 mL/d	Cats fed a dry diet had ↑ FWI: DMI ratio, but ↓ TWI: DMI ratio, and ↓ water turnover: DMI ratios.	Seefeldt and Chapman, (1979)
Healthy mixed breed adult cats (n = 18 females)	(1) Dry + 0.4% NaHSO4 (6.5% moisture) (2) Dry + 0.6% NaHSO4 (6.7% moisture) (3) Dry + 0.8% NaHSO4 (6.8% moisture) (4) Dry + 0.4% H3PO4 (6.8% moisture) (5) Dry + 0.6% H3PO4 (6.6% moisture) (6) Dry + 0.8% H3PO4 (7.0% moisture)	RBD; 7d/leg	Laboratory—individual experimental cages	FWI: 56.4–78.4 mL/d	USG: 1.046–1.060 pH: 6.16–6.49	None.	Spears et al., (2003)
Healthy adult cats (n = 8; 5 females and 3 males)	(1) Dry (% moisture unsp.) + room temperature water (2) Dry (% moisture unsp.) + cool water	Single group CO; 7d/leg	Indoor client-owned	FWI: 142.3–204.0 mL/d	NP	Four of eight cats provided water cooled with ice cubes had ↑ FWI.	Tatliağiz and Akyazi (2023)
Healthy adult male DSH cats (n = 8 males)	(1) Wet (82 % moisture) (2) Freeze-dried (4 % moisture) (3) Dry (3% moisture) (4) Dry + water (70% moisture)	LS; 21d/leg	Laboratory—group cat colony during adaptation; individual during collection period	TWI: 109.2–293.0 mL/d FWI: 0.7–161.5 mL/d	USG: 1.028–1.064 UE: 61.5–228.2 mL/d Fecal moisture: 66.7–72.6 %	Cats fed a wet diet had ↑ TWI and ↑ UE, ↓ FWI, and ↓ USG.	Thomas et al. (2017)
Healthy adult cats (n = 8 mixed sex)	(1) Dry (7.0% moisture) (2) Dry (7.4% moisture) (3) Dry (7.4% moisture) (4) Dry (7.7% moisture) (5) Dry (6.4% moisture) (6) Dry (6.8% moisture) (7) Wet (77.4% moisture) (8) Wet (79.4% moisture) (9) Wet (74.9% moisture)	Single group CO; 14–21 d/leg	Laboratory—individual metabolic cages	TWI: 27.1–51.2 mL/kg/d	USG: 1.026–1.058 UE: 64.8–154.4 mL/d pH: 5.76–7.16 CaOx: 3.5–18.3	In general, cats on a wet diet had ↑ TWI, ↑ pH, ↓ USG, and ↓ CaOx	Wagner et al. (2006)
Healthy adult DSH cats (n = 18 mixed sex)	(1) Dry (% moisture unsp.) + NW (2) Dry (% moisture unsp.) + TW	Parallel; 56d	Laboratory—group cat colony	TWI: 24.3–37.5 mL/kg/d	USG: 1.031–1.058 Urine mOsm/L: 1,337–2,402 pH: 6.19–6.55 Urea: 2.3–4.6 g/dL	Cats that consumed NW had ↑ TWI, ↑ mOsm, ↓ USG, and ↓ urea	Zanghi et al., (2018a)
Healthy adult DSH cats (n = 36 mixed sex)	(1) Dry (% moisture unsp.) + NWP (2) Dry (% moisture unsp.) + NW (3) Dry (% moisture unsp.) + TW	Between subject repeated measures; 44d	Laboratory—individual rooms	TWI: 79–200 mL/d during baseline	USG: 1.021–1.055 UE: 7.4–27.5 mL/kg/d	Cats that consumed NW and NWP had ↑ TWI (relative to the quantity of treatment), ↑ UE, and ↓ USG	Zanghi et al., (2018b)

^*Free water intake was reported if total water intake (free water and food moisture) was not available.

Abbreviations: ↑ = significant increase; ↓ = significant decrease; AA = amino acid; Ca = calcium; CaOx; calcium oxalate; CGM = corn gluten meal; CO = cross-over; CRD = completely randomized design; CP = crude protein; d = day; DMI = dry matter intake; DSH = domestic short hair; FWE = fecal water excretion; FWI = free water intake; IL = indispensable loss; LS =Latin square; MAP = magnesium ammonium phosphate; mOsm = osmolality; MW = metabolic water; NP = not provided; NW = nutrient-enriched water; NWP = nutrient-enriched water with poultry; OCE = operant conditioning experiment; PCV = packed cell volume; PT = preference test; RBD = randomized block design; RCBD = randomized complete block design; RSS = relative supersaturation; SPF = specific pathogen free; TW = tap water; TWE = total water excretion; TWI = total water intake; UE = urine excretion; unsp = unspecified; USG = urine specific gravity; y = year.

Average daily water intake

Of the included studies, 15/32 (47%) reported TWI and 22/32 (69%) reported FWI. Only 4/32 (12.5%) of studies included metabolic water (MW) in the estimated TWI. The average daily TWI of healthy cats across five and eight studies was 22.8 to 51.2 mL/kg BW and 70.0 to 293.0 mL, respectively. The average daily FWI of healthy cats across five and sixteen studies was 16.8 to 50.2 mL/kg BW and 0.7 to 244.6 mL, respectively. One additional study reported the estimated FWI (171 mL on average) of clinically dehydrated cats 48 hours after being provided with nutrient-enriched water (NW) (Peralta et al., 2025) (Table 2).

Table 2.

Range of reported values for total and free water intake and urine volume, specific gravity, pH, osmolality, calcium oxalate, and struvite in healthy cats

Parameter	Lowest value	Highest value	Number of studies (n)
Water intake
TWI (mL/kg BW/d)	22.8	51.2	5
TWI (mL/d)	70.0	293.0	8
FWI (mL/kg BW/d)	16.8	50.2	5
FWI (mL/d)	0.7	244.6	16
Urine
Volume (mL/kg/BW d)	9.2	25.0	7
Volume (mL/d)	20.6	228.2	9
USG	1.021	1.069	16
pH	5.8	7.4	12
Osmolality (mOsm/L)	250.0	3231.0	4
CaOx RSS	0.3	18.3	7
Struvite RSS	2.01	7.75	2

Abbreviations: CaOX = calcium oxalate; FWI = free water intake, RSS = relative supersaturate; TWI = total water intake; USG = urine specific gravity.

Measures of hydration status

Hydration status was most measured using urine specific gravity (USG) (16/32; 50% of papers), with reported USG values ranging from 1.021 to 1.069 (Table 3). All (16/16; 100%) studies reported USG values greater than 1.035 for at least one experimental group, and only 4/16 (25.0%) reported USG values equal to or less than 1.035 for at least one experimental group (Supplementary Table 1). Urine excretion (UE) volume was also reported in 16/32 (50%) of studies, with an average urine volume range of 9.2–25.0 mL/kg BW/d (across 7/16; 44% of studies) and 20.6–228.2 mL/d (across 9/16; 56% of studies). Urinary pH was reported in 12/32 (37.5%) studies, with an average range of 5.76 to 7.40. In the twelve studies that reported urinary pH, 1/12 (8%), 4/12 (33%), 6/12 (50%), and 1/12 (8%) had at least one treatment group with an average pH of <6.0, >6.5, and 6–6.5 as well as both <6.0 and >6.5, respectively. The other main physiological markers of hydration status and/or renal health included urine osmolarity (mOsm), CaOx relative supersaturation (RSS), and struvite RSS. Urine mOsm was reported in 4/32 (12.5%) studies, with an average range of 250.0 to 3,231 mOsm/L. CaOx RSS was reported in 7/32 (22%) studies, with an average range of 0.3 to 18.3. Struvite was reported in 2/32 (6%) studies, with an average range of 2.01 to 7.75 (Table 2). One study measured several indices of renal health and hydration, including serum osmolarity (mOsm), creatinine, urea, cholesterol, triglycerides, albumin, glucose, calcium, urine pH, specific gravity (SG), protein-to-creatinine ratio, calcium, CaOx ratio, and struvite (Hall et al., 2021). Cats that consumed 42.0 to 52.1 mL/kg BW of total water daily had a USG less than 1.035, which only occurred in groups of cats fed wet diets or a dry diet + NW supplement.

Table 3.

The relationship between total water intake and urine specific gravity in cats across an assessment of 16 studies with 34 different treatment groups

	USG
Average TWI (mL/kg BW/d)	≤1.019	1.020–1.029	1.030–1.039	1.040–1.049	1.050–1.059	≥ 1.060
≤ 9.9
10.0–19.9
20.0–29.9				X	XXX	XX
30.0–39.9			X	X	XXXX	XXXX
40.0–49.9			XX	X
≥ 50.0		XX
Average daily TWI (mL/d)
≤ 29.9
30.0–59.9
60.0–89.9					XX
90.0–119.9					XXXXX	X
120.0–149.9			X
150.0–179.9				X	X
≥ 180.0		X

The number of X’s represents the number of studies that report these values.

Abbreviations: TWI = total water intake; USG = urine specific gravity.

Effect of diet or supplementation

The most researched dietary interventions affecting water intake in cats were diet format, specifically wet versus dry diets (8/32; 25% of studies), and protein level, specifically high-versus low-protein diets (5/32; 16% of studies). The most researched supplement affecting water intake in cats was salt (3/32; 9% of studies). Cats fed high-protein and/or high-salt diets have greater water intake when compared to cats fed low-protein and/or salt diets. On the contrary, fat did not increase water intake. Other dietary interventions that appeared to increase water intake included phosphorus (Dobenecker et al., 2018), 1% methylcellulose (added to water to increase its viscosity) (Hall et al., 2021), amino acids (in an AA-purified diet) (Kane et al., 1981), and NW (Zanghi et al., 2018a, 2018b). Fat (Kane et al., 1987; Carciofi et al., 2005), fiber (Armbrust et al., 2003), selenium (Hooper et al., 2018), sodium bisulphate, and phosphoric acid (Spears et al., 2003) did not affect the water intake of cats.

Effect of water source and temperature

The impact of water source and temperature was presented in 3/32 (9%) and 1/32 (3%) of studies, respectively. Cats did not appear to prefer moving or flowing water sources (Grant, 2010; Pachel and Neilson, 2010; Robbins et al., 2019). One study found that 4 of 8 cats preferred cool water to room-temperature water (Tatliağiz and Akyazi, 2023).

Discussion

Daily water intake and hydration status of cats

To our knowledge, this is the first scoping review to describe the extent to which cat hydration research has been conducted, the reported average daily water intake of domestic cats, and whether feline water intake requirements have been identified. While studies that included cats with urinary and renal disease were within the scope of the review, there were no reports on water intake for these groups. Only one of the studies included in this review that included TWI on an mL/kg or g/kg BW basis (1/32; 3%) reported TWI greater than 50 mL/kg. Across an assessment of five and eight papers, healthy domestic cats drank 22 to 51 mL/kg BW and 70 to 293 mL of water daily, respectively. Notably, the reported TWI often did not include MW. Approximately 1.071, 0.566, and 0.396 grams of MW are estimated to be produced per gram of oxidized fat, starch, and protein, respectively (Anderson, 1982). However, to accurately and precisely calculate the MW product, macronutrient oxidation must be measured using indirect calorimetry or stable isotope methodology.

Importantly, the presented TWI of cats is below the currently recommended requirement of 50–60 mL/kg BW. The average USG across an assessment of 34 groups of cats was often greater than 1.035, with most groups averaging from 1.050 to 1.059. From the data extracted in the current review, all cats on a dry diet had an average USG greater than 1.035, except those supplemented with NW. Furthermore, healthy cats fed a wet urinary health diet for 21 d had a TWI of 42.0 mL/kg BW/d and a USG of 1.031 compared to a TWI of 34.0 mL/kg BW/d and a USG of 1.054 when fed a dry urinary diet (Blanchard et al., 2022). Additional studies report that cats fed an exclusively dry commercial diet had a 2.64 times greater risk of developing feline lower urinary tract disease (FLUTD) compared to those fed a mixed (canned and dry) (Piyarungsri et al., 2020) or a 6.90 to 15.87 greater risk than when fed an exclusively canned (Willeberg, 1984; Kennedy and White, 2022) diet. A retrospective assessment of 385 cats with FLUTD reported that 34% were fed a dry diet, 42% a mixed diet, and 4% an exclusively canned diet (Lew-Kojrys et al., 2017). Cats with a FLUTD diagnosis fed a canned and acidified diet, to reduce crystal formation, also had lower USG values and showed greater improvement from baseline compared to cats fed a dry acidified diet (1.039 and 1.051 after 12 mo, respectively) (Markwell et al., 1999). These results may suggest that cats with pre-existing or at-risk of developing FLUTD may benefit from a diet with higher moisture content, such as wet (canned), semi-moist (meat chunks in gravy or jelly), or fresh (lightly cooked) food. Further, in a study of 1,290 client-owned cats, cats diagnosed with calcium oxalate (CaOx) urolithiasis consumed diets with lower moisture content (21% on average) than healthy control cats (32% on average) (Lekcharoensuk et al., 2001). These data combined suggest that groups of cats that consumed 42.0 to 52.1 mL/kg BW of total water appeared to be at lower risk of developing FLUTD and urolithiasis, as indicated by a greater TWI and lower USG. Importantly, none of the papers included in this review reported a USG below 1.019, which is commonly observed in humans (Armstrong and Johnson, 2018) and supports the evolution of carnivores’ ability to concentrate urine.

In the present review, half of the assessed papers that reported pH contained values fell within the accepted range of 6.0–6.6. However, dietary composition, including mineral content and the addition of urinary acidifiers, can help maintain a urine pH within an acceptable range (Markwell et al., 1998; Markwell et al., 1999; Funaba et al., 2001; Spears et al., 2003; Pires et al., 2013). Struvite crystals are soluble in urine with a pH of 6.5 or less (Jacobs et al., 2001), and cats with CaOx urolithiasis were more likely to have a urine pH of less than 6.29 (Kirk et al., 1995). However, it is generally recommended to maintain the urine pH of cats between 6.0 and 6.6 to prevent crystal formation and promote urinary health in cats (Spears et al., 2003). Despite this recommendation, the direct relationship between water intake and urine pH in cats remains unclear. As expected, studies that collected both water intake and UE data reported a positive association (Hashimoto et al., 1995; Hashimoto et al., 1996; Hawthorne and Markwell, 2004; Carciofi et al., 2005; Buckley et al., 2011; Thomas et al., 2017; Zanghi et al., 2018b; Garcia et al., 2021; Blanchard et al., 2022). One study reported a strong and moderate correlation between FWI and water intake from food (r = 0.6348) and UE (r = 0.4487), respectively (Pires et al., 2013). Another study found similar results and identified a positive linear relationship between TWI and UE (Zanghi et al., 2018b). Both water intake and UE were highly variable across and within studies.

The effect of diet format

While there is considerable variation in the reported average daily water intake of cats, diet format, protein and amino acids, salt, phosphorus, and osmolytes (NW), as well as water viscosity, appear to influence the water intake of cats. In general, cats fed a wet diet have higher TWI but lower FWI compared to cats fed a dry diet (Kane et al., 1981; Carciofi et al., 2005; Buckley et al., 2011; Thomas et al., 2017). In contrast, one study reported a lower TWI compared to cats fed a dry diet (Seefeldt and Chapman, 1979); however, these cats were not fed isoenergetically and had a greater dry matter intake (DMI) when on the dry diet. Additionally, the diet composition was not reported, which could have influenced these results and precludes further analyses.

Previous research has suggested that cats have a low thirst drive since they do not compensate their free water intake based on the moisture content of the diet, and instead, the DM (Anderson, 1982); however, this is not fully supported. In some instances, even when the water consumed from a wet diet exceeded the TWI of cats fed dry diets, cats on wet diets still consumed additional free water (Seefeldt and Chapman, 1979; Anderson, 1982; Goggin et al., 1998; Thomas et al., 2017). In contrast, in one study, after 1 d of transitioning from a dry to a wet food diet, cats no longer drank free water (Kane et al., 1981). While it is estimated that cats may have a lower thirst drive compared to most other mammals, considering their evolution from desert-dwelling species, controlled behavioral tests (such as a push-door test) are required to determine cats’ motivation to access free water.

The effects of diet composition

In one study, cats fed a high-protein and high-sodium diet had increased water intake compared to those fed moderate-protein and low-sodium diets; however, the highest protein diets (64% and 52% crude protein; CP) had a moisture content of ∼5%, compared to ∼6% for the lowest protein diet (28% CP) (Garcia et al., 2021). Still, these results are consistent when protein and salt were tested alone. Feeding healthy cats a high-salt diet (∼1% DM Na and ∼2% DM Cl) did not impact blood pressure; however, it increased FWI and urine mOsm and decreased USG compared to cats fed a low-salt diet (∼0.5% DM Na and ∼1% DM Cl) (Luckschander et al., 2004). These results are consistent in aging cats, where senior cats fed a high-salt diet (3.1 g/Mcal sodium, 5.5 g/Mcal chloride) did not have an increased risk of poor cardiac function when compared to cats fed a low-salt diet (1.0 g/Mcal sodium, 2.2 g/Mcal chloride) (Chetboul et al., 2014). In humans, providing a diet that is too low in sodium can lead to an increase in plasma renin activity (PRA), which helps regulate blood pressure (Graudal et al., 2021). Furthermore, blood pressure and weight gain are associated with “very high” sodium diets in humans, with aldosterone being maximally suppressed when sodium intake reaches 800 mEq/d (Murray et al., 1978). Currently, there is no evidence to suggest that high-salt intake leads to dysregulated aldosterone secretion and increased plasma renin activity in healthy cats. In one study, plasma aldosterone levels were higher in cats fed a low-sodium diet for two weeks than in cats fed a high-sodium diet for 2 wk (Luckschander et al., 2004). Therefore, feeding healthy cats a high-salt diet appears to be effective in increasing their water consumption, without causing a negative impact on cardiac health. Indeed, there are commercial diets that use higher levels of salt to increase water intake and improve hydration and USG.

Cats fed high-protein diets (65% crude protein; CP) compared to cats fed a low protein diet (26% CP) with the same level of salt (Hashimoto et al., 1995), and cats fed high-salt diets (11.51–16.74 g Na/MJ) compared to cats fed low-salt diets (<7.32 g Na/MJ) with the same level of protein (Hawthorne and Markwell, 2004) had increased water consumption. Protein consumption has been previously associated with water consumption in broiler chickens (Marks and Pesti, 1984), pigs (Pfeiffer et al., 1995; Shaw et al., 2006), and rats (Kaunitz et al., 1956; Johnson et al., 1989). In mammals, protein metabolism generates urea, a form of nitrogenous waste that requires water for transport and elimination (Klein et al., 2011). Increased protein consumption increases urea excretion (Fouillet et al., 2008; Bankir et al., 2015; Weiner et al., 2015), and therefore, increased protein intake and urinary water loss may lead to greater water intake in some mammals. However, unlike the studies mentioned above, in humans, consuming 3.6, 1.8, and 0.8 g/kg of protein per day did not appear to affect fluid intake, and high-protein consumption did not impact hydration status in healthy adult males (Martin et al., 2006). Furthermore, high-protein consumption can lead to increased urinary excretion of phosphorus in cats (Hashimoto et al., 1995; Hashimoto et al., 1996).

In addition to protein, dietary amino acid content may impact the water intake and hydration status of cats; however, further exploration is required. In one study, cats fed a dry amino acid (AA)-purified diet had a greater FWI than those fed a commercial wet diet, but not a casein-purified diet, and a lower FWI than those fed a commercial dry diet (Kane et al., 1981). Notably, the diets were inconsistent in composition, and the AA profile was provided only for the AA-purified diet. While the purpose of this study was to assess the diurnal feeding and drinking patterns of cats fed four different dietary formats, supplementation with AAs to increase water intake and improve hydration status is well documented in rats and humans. In a study of 20 temporarily dehydrated men and women, the consumption of an electrolyte-carbohydrate beverage, an electrolyte-branched chain AA beverage, or flavored water all improved hydration status immediately after rehydration (as evidenced by a decrease in USG); however, after 4 hr of rehydration, USG returned only to baseline post electrolyte-branched AA chain consumption, suggesting greater intercellular rehydration (Tai et al., 2014). This said, not all AA provide the same hydration benefits. For example, rats supplemented with a mixture of arginine (Arg) + methionine (Met) + valine (Val) (0.38 g total), Arg + histidine (His) + lysine (Lys) (0.44 g total), as well as Arg (0.15 g) and His (0.10 g) alone had a greater FWI when compared to rats fed a control diet; however, no effect on water intake was observed when rats were supplemented with a mixture of phenylalanine (Phe) + tyrosine (Tyr) + tryptophan (Trp) + threonine (Thr) (0.46 g total), isoleucine (Ile) + leucine (Leu) + Val (0.45 g total), or Lys (0.25 g) alone (Anderson et al., 1994). Notably, previous research provides evidence of AVP stimulation following Arg and His supplementation (Charnogursky et al., 1990; Smith and Armstrong, 1996; Bologna et al., 2020), which may suggest increased thirst and explain the increased water intake observed in the rats in the above study.

While water intake of cats can be increased by increasing the protein content of a diet, no relationship has been found between dietary fat consumption and water intake. One study reported that cats fed a high-fat diet (45% fat) did not consume more water or alter their drinking patterns compared to cats fed a low-fat diet (15% fat) (Kane et al., 1987). However, the supplementation period for the low-fat diet was only 10 d, compared to 21 d for the high-fat diet. Body weight was also not reported. A further study reported that cats fed a moderate-fat and protein diet (with or without added water) or a high-fat and protein diet did not differ in TWI (Carciofi et al., 2005). In contrast, reduced water consumption by humans has been associated with increased fat consumption (a 1% decrease in water consumption for every additional 0.17–0.25 g of fat) (An and McCaffrey, 2016). Similarly, rats fed a high-fat diet had a lower FWI per kg BW when compared to rats fed a low-fat diet for six weeks, and FWI was found to be regulated by the glucagon-like peptide-1 (GLP-1) pathway (Volcko et al., 2020). In a separate, but similar study, rats fed a high-fat diet for nine weeks had greater white adipose tissue mass than those fed a control diet; however, after 48 hr of dehydration, white adipose tissue mass decreased (Dos‐Santos et al., 2022). Therefore, the reduced FWI by groups fed high-fat diets may be associated with increased metabolic water production; however, since body weight was not reported in the aforementioned study, further exploration is required in cats.

In one study, providing a high-phosphorus diet (16.0 g/kg DM) to cats appeared to increase TWI when compared to a low-phosphorus diet (5.6 g/kg/DM); however, cats on the high-phosphorus diet al.o had increased DMI (Dobenecker et al., 2018). Therefore, phosphorus alone is unlikely to have caused the increased water consumption observed. The relationship between increased DMI and increased water intake has been observed in a variety of mammals, including beef cows (Blake et al., 2023), dairy cows (Kramer et al., 2008; Lukas et al., 2008), horses (Ellis et al., 2002; Freeman et al., 2021), rabbits (Tschudin et al., 2011), and rats (Adolph, 1947; Strominger, 1947; Cizek and Nocenti, 1965). Additionally, providing high-phosphorus diets may increase the production of urinary crystals or be harmful to cats with CKD. For example, cats fed a diet with 1.6% phosphate (provided by sodium monobasic phosphate) had greater urinary phosphate concentrations and a higher prevalence of urinary crystals when compared to cats fed a diet with ∼0.6% phosphate provided by the same source (Lewis et al., 1978). Based on an odds ratio test, cats on diets with 1.77–2.79, 2.80–3.16, and 3.17–4.70 mg/kcal of phosphorus were 1.88, 3.07, and 2.50 more likely to develop magnesium ammonium phosphate (MAP) or struvite uroliths, when compared to diets with 0.85–1.76 mg/kcal phosphorus, respectively (Lekcharoensuk et al., 2001). In a study of 191 human patients aged 20 or older with CKD, those with a urinary phosphorus excretion of 11.16–17.07 mg/d per creatinine clearance (CCr), 17.08–29.61 mg/d/CCr, and ≥ 29.62 mg/d/CCr had a 2.56, 7.53, and 12.17 greater risk of CKD progression compared to those with a urinary phosphorus excretion of ≤ 11.15 mg/d/CCr (Kawasaki et al., 2015). Creatinine clearance was also reduced in cats fed diets high in phosphorus (Pastoor et al., 1995; Dobenecker et al., 2018), suggesting an additional risk factor for cats with CKD.

The effect of supplementation in water

Methylcellulose can be added to water as an emulsifying agent and to increase water viscosity (Gullapalli and Sheth, 1996; Nokhodchi et al., 1997). Given the lapping mechanics of a cat’s tongue previously described, increasing the viscosity of the water may result in greater water uptake per lap. A comparison of drinking duration versus volume of water consumed, or modeling the lapping mechanics of cats provided with viscous water versus a control, is required to assess this hypothesis. In one study, NW was administered to clinically dehydrated cats for 48 hr (Peralta et al., 2025). While owners reported an increase in quality-of-life assessment, and veterinarians reported improved hydration scores, physiological markers of hydration did not show significant improvement. The lack of substantial improvement in the hydration status of these cats may be attributed to the short duration of the supplementation period. In addition, while the cats appeared to drink the NW well and consumed greater volumes than with untreated water, this may be attributed to the delivery format, in which owners were instructed to offer 1–3 pouches. In additional studies, NW has been shown to increase water consumption and improve hydration status (as evidenced by a lower USG) in healthy cats (Zanghi et al., 2018a, 2018b) and dogs (Zanghi and Gardner, 2018; Niedermeyer et al., 2020).

The effect of water source and temperature

It is a common belief that cats prefer moving water sources (such as free-flowing or circulating), which may lead to increased water intake and, subsequently, improved hydration. However, this is not well supported by current scientific research. While a few individual cats showed a preference for moving water, water intake was not affected (Grant, 2010; Pachel and Neilson, 2010; Robbins et al., 2019). Initially, FWI appeared to increase in cats provided with a fountain compared to those with a static bowl; however, after removing a cat that did not adhere to the protocol (the owner had added wet food to the dry diet during the static bowl treatment), no difference was reported (Grant, 2010). Notably, although the diet format remained consistent for the remaining cats in the study, the diet composition was not reported. This finding is consistent with additional research, where FWI was similar in cats supplied with a circulating fountain, a free-falling fountain, or a static bowl (Robbins et al., 2019). Cats in this study were individually housed in cages, which does not replicate a standard at-home environment and may have additionally affected water intake due to acute stress. Subsequent research on water intake and water-source preference in cats fed a consistent diet format and in a setting that better represents client-owned cats is warranted.

One study investigating the impact of water temperature reported that four of the eight cats included in the study showed a greater intake of cooled water compared to room temperature water, while no cats had a greater intake of room temperature water compared to cooled water (Tatliağiz and Akyazi, 2023). However, inappropriate statistics were used, and water intake should be compared across groups and not on an individual cat basis. Further, environmental conditions were not controlled across treatments, and the temperature of the cooled water was not maintained. Previous research has reported that humans increase their FWI when the water temperature increases from 0 to 15°C and decrease their FWI at temperatures above 15°C (Boulze et al., 1983). Similarly, during a period of exercise-induced dehydration, healthy male volunteers consumed a greater volume of cool water (15°C) than warm water (40 °C) (Hubbard et al., 1984). In one study of mixed-breed dogs subjected to a three-bowl test, cool water intake (15°C) was greater than that of room temperature (25°C) and warm (35°C) water (Sydenham et al., 2005). The preference for cold water is related to improved taste and the ability to mask unwanted flavors, as shown in rats (Kay et al., 2020). Consuming cold water may also promote gastric efficiency. Gastric contractions were slower and more regulated in adult men who drank water cooled to 2°C than after drinking water warmed to 60 °C (Fujihira et al., 2020), suggesting improved gastric modulation and a physiological benefit to cold water consumption. To accurately determine cats’ water temperature preferences, studies with controlled environmental conditions and maintained water temperatures should be conducted.

Conclusion

There is a dearth of knowledge on cat hydration, particularly regarding the relationship between water intake and physiological indicators of hydration status, as well as cat drinking behavior. However, some key results were identified in this review. The average TWI of cats ranged from 23 to 51 mL/kg BW daily, which is below the current recommended NRC (2006) guidelines. Dietary treatments (moisture content, high protein, amino acids, salt, and osmolytes), as well as water viscosity, can increase the water intake of cats. Cats fed a wet diet or supplemented with NW had a TWI of 42.0 to 52.1 mL/kg BW, resulting in a USG ≤ 1.035. These results provide evidence of the minimum water intake required for optimal hydration in cats; if this requirement cannot be met, these cats would likely benefit from a high-moisture diet. Several knowledge gaps and opportunities for future studies have been identified, including (1) The impact of diet format on water intake of cats fed isoenergetic quantities (2) daily variation in urinary biomarkers of cats, such as USG, in response to dietary treatment (3) the minimum water intake required before cats are at an increased risk of developing renal or urinary disease, (4) the effect of AA composition as a metric of total nitrogen or protein on water intake and hydration of cats, and (5) the impact of water format (flowing, circulating, still) on water intake and preference of client-owned cats.

Abbreviations:

AA,

amino acid

Arg,

arginine

AVP,

arginine vasopressin

BW,

body weight

Ca,

calcium

CaOx

calcium oxalate

CGM,

corn gluten meal

CKD,

chronic kidney disease

CO,

cross-over

CRD,

completely randomized design

CP,

crude protein

DMI,

dry matter intake

FLUTD,

feline lower urinary tract disease

FWE,

fecal water excretion

FWI,

free water intake

His,

histidine

IL,

indispensable loss

Ile,

isoleucine

Leu,

leucine

LS,

Latin square

Lys,

lysine

Met,

methionine

mOsm,

osmolality

MW,

metabolic water

NW,

nutrient-enriched water

NWP,

nutrient-enriched water with poultry

OCE,

operant conditioning experiment

PRA,

plasma renin activity

PCV,

packed cell volume

Phe,

phenylalanine

PT,

preference test

RBD,

randomized block design

RCBD,

randomized complete block design

RSS,

relative supersaturation

SPF,

specific pathogen free

Thr,

threonine

Trp,

tryptophan

Tyr,

tyrosine

TWE,

total water excretion

TWI,

total water intake

UE,

urine excretion

USG,

urine specific gravity

Val,

valine

WI,

water intake

Acknowledgments

This work was funded by Peturio Holdings, LLC, DBA Cat Years. However, this financial support did not influence the conduct of this study or the interpretation of the data.

Author Contributions

Pauline Angela Louise Kosmal (Conceptualization, Data curation, Formal analysis, Methodology, Visualization, Writing—original draft, Writing—review & editing), Genevieve Gillies (Conceptualization, Methodology, Writing—review & editing), Lawrence E. Armstrong (Methodology, Writing—review & editing), and Anna K. Shoveller (Conceptualization, Data curation, Methodology, Supervision, Writing—review & editing).

Supplementary Data

Supplementary data are available at Journal of Animal Science online.

Conflict of interest statement

. P.A.L.K. and G.G. declare no conflict of interest. A.K.S. has received honoraria and research funding from various pet food manufacturers, ingredient suppliers, and provincial and federal granting agencies. They declare that they serve on the Scientific Board of Champion Petfoods. L.E.A. serves as a paid consultant and Advisory Board member for Peturio Holdings, LLC, DBA Cat Years.