Field Water Disinfection

▸. RISK AND ETIOLOGY

Infectious agents in contaminated drinking water with the potential for waterborne transmission include bacteria, viruses, protozoa, and parasites. Risk of waterborne illness depends on the number of organisms consumed, which is determined by the volume of water, concentration of organisms, and treatment system efficiency (Box 44-1, Box 44-2, Box 44-3 ).

Box 44-1. Waterborne Enteric Pathogens.

BACTERIAL

Escherichia coli

Shigella

Campylobacter

Vibrio cholerae

Salmonella

Yersinia enterocolitica

Aeromonas

VIRAL

Hepatitis A

Hepatitis E

Norovirus

Poliovirus

Miscellaneous enterics (>100 types: e.g., adenovirus, enterovirus, calicivirus, ECHO viruses, astrovirus, coronavirus)

Giardia lamblia

Entamoeba histolytica

Cryptosporidium

Blastocystis hominis

Isospora belli

Balantidium coli

Acanthamoeba

Cyclospora

PARASITIC

Ascaris lumbricoides

Ancylostoma duodenale (hookworm)

Taenia spp. (tapeworm)

Fasciola hepatica (sheep liver fluke)

Dracunculus medinensis

Strongyloides stercoralis

Trichuris trichiura (whipworm)

Clonorchis sinensis (oriental liver fluke)

Paragonimus westermani (lung fluke)

Diphyllobothrium latum (fish tapeworm)

Echinococcus granulosus (hydatid disease)

ECHO, enteropathic cytopathogenic human orphan.

Box 44-2. Enteric Pathogens in U.S. Wilderness or Recreational Water.

COMMONLY REPORTED

Giardia

Cryptosporidium

OCCASIONALLY REPORTED WITH FIRM EIDENCE FOR WATERBORNE

Campylobacter

Hepatitis A

Hepatitis E

Enterotoxigenic Escherichia coli

E. coli 0157:H7

Shigella

Enteric viruses

UNUSUAL OCCURRENCES, WATERBORNE SUSPECTED

Yersinia enterocolitica

Aeromonas hydrophila

Cyanobacterium (blue-green algae)

Box 44-3. Water Quality: Key Points.

• •In wilderness water, most sediment is inorganic and clarity is not an indication of microbiologic purity.
• •In general, cloudiness indicates higher risk of contamination.
• •A major factor determining the amount of microbe pollution in surface water is human and animal activity in the watershed.
• •Streams do not purify themselves.
• •Settling effect of lakes may make them safer than streams, but care should be taken not to disturb bottom sediments when obtaining water.
• •Groundwater is generally cleaner than surface water because of the filtration action of overlying sediments.

Relative susceptibility of microorganisms to heat: protozoa > bacteria > viruses.

▸. DEFINITIONS

• 1.Disinfection, the desired result of field water treatment, means the removal or destruction of harmful microorganisms.
• 2.Pasteurization is similar to disinfection but specifically refers to the use of heat, usually at temperatures below 100° C (212° F), to kill most pathogenic organisms.
• 3.Disinfection and pasteurization should not be confused with sterilization, which is the destruction or removal of all life forms.
• 4.The goal of disinfection is to achieve potable water, indicating only that a water source, on average over a period of time, contains a “minimal microbial hazard” so that the statistical likelihood of illness is acceptable.
• 5.Water sterilization is not necessary because not all organisms are enteric human pathogens.
• 6.Purification is the removal of organic or inorganic chemicals and particulate matter to remove offensive color, taste, and odor. The term is frequently used interchangeably with “disinfection,” but purification may not remove or kill enough microorganisms to ensure microbiologic safety (Box 44-4 ).

Box 44-4. Heat.

ADVANTAGES

• •Does not impart additional taste or color to water
• •Single-step process that inactivates all enteric pathogens
• •Efficacy is not compromised by contaminants or particles in the water, as happens with halogenation and filtration
• •Can pasteurize water without sustained boiling

DISADVANTAGES

• •Does not improve the taste, smell, or appearance of poor-quality water
• •Fuel sources may be scarce, expensive, or unavailable
• •Does not prevent recontamination during storage

▸. HEAT

• 1.The boiling time required is important when fuel is limited.
• 2.Enteric pathogens including cysts, bacteria, viruses, and parasites can be killed at a temperature well below boiling.
• 3.Thermal death is a function of both time and temperature; therefore lower temperatures are effective with longer contact times
• 4.Microorganisms have varying sensitivity to heat; however, all common enteric pathogens are readily inactivated by heat (Table 44-1 ).
• 5. Given its environmental stability and clinical virulence, hepatitis A virus is a special concern. It should respond to heat as do other enteric viruses, but data indicate that it has greater thermal resistance.
• 6.The boiling point decreases with the lower atmospheric pressure present at high elevations (Table 44-2 ). Because heat inactivation occurs below typical boiling temperatures, elevation should not make a large difference (unless hepatitis A is of concern).
• 7.The 10-minute boiling rule is for the sterilization of water including the destruction of heat-resistant bacterial spores, which are generally not enteric pathogens. Disinfection of water requires less than 10 minutes. Pasteurization of food and beverages is accomplished at 65° C (150° F) for 30 minutes or at 71° C (160° F) for 1 to 5 minutes. Enteric pathogens are killed within seconds by boiling water and rapidly at temperatures above 60° C (140° F). The majority of the time required raising the temperature of water to the boiling point works toward disinfection, so water is safe to drink by the time it has reached a full boil. For an extra margin of safety (e.g., hepatitis A), keep the water covered and hot for several minutes after boiling or boil for 1 full minute (up to 3 minutes at high altitude).
• 8.A pressure cooker saves time and fuel at all elevations.
• 9.Pasteurization has been successfully achieved using solar heating. A solar cooker constructed from a foil-lined cardboard box with a glass window in the lid can be used for disinfecting large amounts of water by pasteurization. This could be a low-cost method for improving water quality, especially in refugee camps and disaster areas (see “Ultraviolet Light” later; Tables 44-1 to Table 44-2; Box 44-5 ).

TABLE 44-1.

Data on Heat Inactivation of Microorganisms as Reported in the Literature

ORGANISM	LETHAL TEMPERATURE/TIME
Giardia	55° C (131° F) for 5 min 100° C (212° F) immediately 50° C (122° F) for 10 min (95% inactivation) 60° C (140° F) for 10 min (98% inactivation) 70° C (158° F) for 10 min (100% inactivation) 55° C (131° F)
Entamoeba histolytica	Similar to Giardia
Nematode cysts, helminth eggs, larvae, cercariae	50–55° C (122–131° F)
Cryptosporidium	45–55° C (113–131° F) for 20 min 55° C (131° F) warmed over 20 min 64.2° C (148° F) within 2 min 72° C (162° F) heated up over 1 min
Escherichia coli	55° C (131° F) for 30 min 60–62° C (140–144° F) for 10 min
Salmonella and Shigella	65° C (149° F) for <1 min
Vibrio cholerae	60–62° C (140–144° F) for 10 min 100° C (212° F) for 30 sec
E. coli, Salmonella, Shigella, Campylobacter	60° C (140° F) for 3 min (3-log reduction) 65° C (149° F) for 3 min (all but few Campylobacter) 75° C (167° F) for 3 min (100% kill)
E. coli	50° C (122° F) for 10 min ineffective 60° C (140° F) for 5 min 70° C (158° F) for 1 min
Viruses	55–60° C (131–140° F) within 20–40 min 70° C (158° F) for >1 min
Hepatitis A	98° C (208° F) for 1 min 85° C (185° F) for 1 min 61° C (142° F) for 10 min (50% disintegrated) 60° C (140° F) for 19 min (in shellfish)
Hepatitis E	60° C (140° F) for 30 min
Bacterial spores	>100° C (212° F)

TABLE 44-2.

Boiling Temperatures at Various Altitudes

ALTITUDE (ft)	ALTITUDE (m)	BOILING POINT
5000	1524	95° C (203° F)
10,000	3048	90° C (194° F)
14,000	4267	86° C (187° F)
19,000	5791	81° C (179° F)

Box 44-5. Summary of Clarification Techniques.

TECHNIQUE	PROCESS USES	ADVANTAGES
Sedimentation	Settling by gravity of large particulates	Requires long time Greatly improves water aesthetics
Coagulation-flocculation	Removes suspended particles, most microorganisms, some dissolved substances	Simple process, easily applied in field Greatly improves water quality Improves efficacy of filtration and chemical disinfection
Activated charcoal	Removes organic and some inorganic chemicals	Removes toxins such as pesticides and removes chemical disinfectants Improves taste of water
Filtration	Physical and chemical process	Removes microorganisms If charcoal stage, may improve taste and remove chemicals

▸. FILTRATION AND CLARIFICATION

Filtration

• 1.Field filters that rely solely on the mechanical removal of microorganisms may be adequate for cysts and bacteria but may not reliably remove viruses, which are a major concern in water where high levels of fecal contamination are present (e.g., in developing countries).
• 2.They have the advantages of being simple and requiring no holding time.
• 3. They do not add any unpleasant taste and may improve taste and appearance of water.
• 4.Most viruses adhere to larger particles or clump together into larger aggregates that may be removed by a filter. However, filtration is not an adequate method to eliminate viruses because the infectious dose of an enteric virus may be quite small. Filters are often expensive and can add considerable weight and bulk to a backpack.
• 5. Some devices are designed as purely mechanical filters, whereas others combine filtration with granular activated carbon (GAC). Most of the filters containing iodine resins have been withdrawn from the market. Currently only one drink-through bottle uses an iodine resin.
• 6.The filter pore size required to remove microorganisms effectively is difficult to determine. Microorganisms possess elasticity and deform under pressure, making it possible for them to squeeze through filter pores. Most field filters are depth filters with maze-like passageways that trap particles and organisms smaller than the average diameter of a passage.
• 7.Being familiar with the functional removal rate of certain organisms rather than with the rated pore size of the filter is more useful and important. Good testing data are necessary to back claims; however, objective comparative data are not generally available.
• 8.The size of a microorganism is the primary determinant of its susceptibility to filtration. Filters are rated by their ability to retain particles of a certain size, which is described by two terms. Absolute rating means that 100% of a certain size of particle is retained. Nominal rating indicates that more than 90% of a given particle size will be retained.
• 9.All filters eventually clog from suspended particulate matter, present even in clear streams, requiring cleaning or replacement of the filter. The ability to easily service a unit in the field is an advantage.
• 10.As a filter clogs, it requires increasing pressure to drive water through it, which can force microorganisms through the filter.

Reverse Osmosis

• 1.A reverse-osmosis filter uses high pressure (100 to 800 psi) to force water through a semipermeable membrane that filters out dissolved ions, molecules, and solids.
• 2.Reverse osmosis is generally used for desalinating water.
• 3.It may also be used to remove biologic contaminants.
• 4.Small hand-pumped reverse osmosis units have been developed. High price and slow output currently limit their use by land-based wilderness travelers.
• 5.Essential survival item for ocean travelers (Box 44-6 ; Table 44-3 ).

Box 44-6. Filtration.

ADVANTAGES

• •Simple to operate
• •Mechanical filters require no holding time for treatment (water is treated as it comes out of the filter)
• •Large choice of commercial products
• •Adds no unpleasant taste and often improves taste and appearance of water
• •Rationally combined with halogens for removal or destruction of all pathogenic waterborne microbes

DISADVANTAGES

• •Adds bulk and weight to baggage
• •Most filters not reliable for removal of viruses
• •Expensive relative to chemical treatment
• •Channeling of water or high pressure can force microorganisms through the filter
• •Eventually clogs from suspended particulate matter; may require some maintenance or repair in field

Susceptibility of microorganisms to filtration: protozoa > bacteria > viruses.

TABLE 44-3.

Microorganism Susceptibility to Filtration

ORGANISM	AVERAGE SIZE (mm)	MAXIMUM RECOMMENDED FILTER RATING (mm)
Viruses	0.03	N/S
Escherichia coli	0.5 × 3–8	0.2–0.4
Campylobacter	0.2–0.4 × 1.5–3.5	Same as above
Microsporidia	1–2	N/S
Cryptosporidium oocyst	2–6	1
Giardia cyst	6–10 × 8–15	3–5
Entamoeba histolytica cyst	5–30 (average 10)	Same as Giardia
Cyclospora	8–10	Same as Giardia
Nematode eggs	30–40 × 50–80	20
Schistosome cercariae	50 × 100	Coffee filter or fine cloth
Dracunculus larvae	20 × 500	Coffee filter or fine cloth

N/S, Not specified.

Clarification of cloudy water can be achieved by sedimentation, coagulation-flocculation (C-F), or adsorption.

• 1.Large particles settle by gravity over 1 to 2 hours in sedimentation. Although filters remove particulate debris, thus improving the appearance and taste of “dirty” water, they clog quickly if the water contains large particles.
• 2.Smaller suspended particles can be removed by coagulation-flocculation (C-F). This is accomplished in the field by adding alum (aluminum potassium sulfate) (Box 44-7 ). Alum is used in the food industry as a pickling powder and is nontoxic. C-F will remove contaminants that cause an unpleasant color and taste, some dissolved metals, and some microorganisms (Table 44-4 ).

Box 44-7. Water Clarification Using Alum.

• 1.Add a pinch of alum to each gallon of water.
• 2.Mix well, stir occasionally for 30 minutes, and then allow 30 to 60 minutes for settling.
• 3.The water should clear; if it does not, add another pinch of alum.
• 4.Decant or pour the water through a paper filter to remove clumps of flocculate.
• 5.Granular activated charcoal (GAC) removes organic pollutants, chemicals, and radioactive particles by adsorption. This improves the color, taste, and smell of the water. Although some microorganisms adhere to GAC or become trapped in charcoal filters, GAC does not remove all microorganisms, so it does not disinfect.
• 6.GAC can be used to remove halogens (iodine, chlorine) after disinfection.
• 7.If GAC is used to remove iodine or chlorine, wait until after the required contact time for disinfection before running water through charcoal or adding charcoal to the water.
• 8.Filters that use iodine resins, followed by GAC, rely on a different dynamic for disinfection.
• 9.Although residual-free iodine is largely removed by GAC, iodine is thought to remain bound to microorganisms following the resin pass-through and GAC pass-through phases.
• 10.The necessary contact time for iodine resins is not absolutely determined, but it is clearly less than that required with standard iodine solutions.

TABLE 44-4.

Factors Affecting Halogen Disinfection

	EFFECT	COMPENSATION
Primary Factors
Concentration	Measured in milligrams per liter (mg/L) or the equivalent, parts per million (ppm); higher concentration increases rate and proportion of microorganisms killed.	Higher concentration allows shorter contact time for equivalent results. Lower concentration requires increased contact time.
Contact time	Usually measured in minutes; longer contact time assures higher proportion of organisms killed.	Contact time is inversely related to concentration; longer time allows lower concentration.
Secondary Factors
Temperature	Cold slows reaction time.	Some treatment protocols recommend doubling the dose (concentration) of halogen in cold water, but if time allows, exposure time can be increased instead, or the temperature of the water can be increased.
Water contaminants, cloudy water (turbidity)	Halogen reacts with organic nitrogen compounds from decomposition of organisms and their wastes to form compounds with little or no disinfecting ability, effectively decreasing the concentration of available halogen. In general, turbidity increases halogen demand.	Doubling the dose of halogen for cloudy water is a crude means of compensation that often results in a strong halogen taste on top of the taste of the contaminants. A more rational approach is to first clarify water to reduce halogen demand.
pH	The optimal pH for halogen disinfection is 6.5 to 7.5. As water becomes more alkaline, approaching pH 8.0, much higher doses of halogens are required.	Most surface water is neutral to slightly acidic, so compensating for pH is not necessary. Tablet formulations of halogen have the advantage of some buffering capacity.

Halogens

Halogens (chlorine and iodine) are effective disinfectants that are active against bacteria, viruses, Giardia, and cysts of amebae, excluding Cryptosporidium. They are readily available and inexpensive.

Concentration and Demand

• 1.Disinfection with halogens depends on both the concentration of halogen and the amount of time the halogen is in contact with the water (contact time). An increase in one allows a decrease in the other.
• 2.Minor factors affecting this method include the water temperature (cold slows reaction time) and presence of organic contaminants in the water, which react with halogen and decrease its disinfectant action.
• 3.Use 4 parts per million (ppm) as a target concentration for surface water and allow extra contact time, especially if the water is cold.
• 4.In cold water, the contact time or dose should be increased; in polluted water, the dose must be increased.
• 5.In cloudy water that will not settle out by sedimentation, the halogen dose should be at least 8 ppm to account for the greater halogen demand that results from the presence of organic material. Ideally, use C-F to clarify the water before halogenation and then use a smaller amount of halogen.

Pathogen Sensitivity

• 1.Bacteria are extremely sensitive to halogens.
• 2.Viruses and Giardia require higher concentrations or longer contact times.
• 3.Certain parasite eggs such as Ascaris are resistant but are not usually spread by water. These types of resistant cysts and eggs are susceptible to heat or filtration.
• 4. Cryptosporidium cysts are extremely resistant to halogens.
• 5.Although Cryptosporidium oocysts have been found in surface water and have been identified as the etiologic agent in cases of travelers' diarrhea and municipal water-borne outbreaks, it is unclear how much risk they pose in pristine wilderness waters.
• 6.The resistance of Cryptosporidium will require an alternative to halogens or a combination of methods to ensure removal and inactivation of all pathogens.

Chlorine versus Iodine

• 1.Compared with chlorine, iodine is less affected by pH or nitrogenous wastes, and it tastes better.
• 2.Chlorine (Table 44-5 ) and iodine (Table 44-6 ) are available in either liquid or tablet form.
• 3.
  Concern surrounds the physiologic activity of iodine.

  • a.
    At levels used for water disinfection, iodine is safe for most people.
  • b.
    Despite iodine's relative safety, some alteration in thyroid function can be measured and some persons experience magnification of existing thyroid problem.
  • c.
    Hypersensitivity reactions to iodine can occur.
  • d.
    Iodine use is not recommended for persons with unstable thyroid disease or a known iodine allergy.
  • e.
    Iodine should not be used during pregnancy for more than several weeks because of the risk of neonatal goiter.
  • f.
    Caution dictates limiting exposure (daily iodination of all drinking water) to periods of 1 month or less.
• 4.
  Iodine resins may reduce toxicity concerns because they leave low concentrations of dissolved iodine in the water. They also allow for the complete removal of iodine residual with GAC. Iodine resins have been incorporated into many different filter designs now available for field use.

  • a.
    Most designs incorporate two stages in addition to the iodine resin. A microfilter, generally 1 micron (μm), effectively removes Cryptosporidium, Giardia, and other halogen-resistant parasitic eggs or larva. Because iodine resins kill bacteria and viruses rapidly, no significant contact time is required for most water.
  • b.
    The addition of a third stage of activated charcoal removes dissolved residual; however, the importance of iodine residual for disinfection has not been established.
• 5.Halogens can be applied with equal ease to large and small quantities of water (TABLE 44-7, TABLE 44-8, TABLE 44-9 ).

TABLE 44-5.

Experimental Data for 99.9% Kill with Chlorine

CONCENTRATION	TIME	pH	TEMPERATURE
Giardia lamblia (consistent with Entamoeba histolytica)
0.5 mg/L	6-24 hr	6-8	3-5° C (37-41° F)
4.0 mg/L	60 min	6-8	3-5° C (37-41° F)
8.0 mg/L	30 min	6-8	3-5° C (37-41° F)
3.0 mg/L	10 min	6-8	15° C (59° F)
1.5 mg/L	10 min	6-8	25° C (77° F)
Enteric Viruses
0.5 mg/L	40 min	7.8	2° C (35.6° F)
0.3 mg/L	30 min	7.8	25° C (77° F)
Escherichia coli
0.03 mg/L	5 min	7.0	2-5° C (35.6-41° F)

TABLE 44-6.

Experimental Data for 99.9% Kill with Iodine

CONCENTRATION	TIME	pH	TEMPERATURE
Giardia and Amebae Cysts
3.0 mg/L	15 min	7.0	20° C (68° F)
7.0 mg/L	30 min	7.4	3° C (37.4° F)
Poliovirus
0.3 mg/L	1.5 min	7.0	25° C (77° F)
Escherichia coli
1.0 mg/L	1 min	6.5–8.5	2–5° C (35.6–41° F)

TABLE 44-7.

Iodine Solutions

PREPARATION	IODINE (%)	IODIDE (%)	TYPE OF SOLUTION
Iodine topical solution	2.0	2.4 (sodium)	Aqueous
Lugol's solution	5.0	10.0 (potassium)	Aqueous
Iodine tincture	2.0	2.4 (sodium)	Aqueous-ethanol
Strong iodine solution	7.0	9.0 (potassium)	Ethanol (85%)

TABLE 44-8.

Water Disinfection Techniques and Halogen Doses

	ADDED TO 1 L OR QUART OF WATER
IODINATION TECHNIQUES	AMOUNT FOR 4 ppm	AMOUNT FOR 8 ppm
Iodine tabs Tetraglycine hydroperiodide EDWGT Potable Aqua Globaline	½ tab	1 tab
2% Iodine solution (tincture)*	0.2 mL or 5 gtts	0.4 mL or 10 gtts
10% Povidone-iodine solution*†	0.35 mL or 8 gtts	0.70 mL or 16 gtts
Saturated solution: iodine crystals in water	13 mL	26 mL
Saturated solution: iodine crystals in alcohol	0.1 mL	0.2 mL

CHLORINATION TECHNIQUES	AMOUNT FOR 5 ppm	AMOUNT FOR 10 ppm
Sodium hypochlorite (household bleach 5%)†	0.1 mL or 2 gtts	0.2 mL or 4 gtts
Calcium hypochlorite (Redi Chlor [1/10 g tab])		¼ tab/2 quarts
Sodium dichloroisocyanurate (AquaClear)		1 tab (8.5 mg NaDCC)
Chlorine plus flocculating agent (Chlor-Floc)		1 tab

EDWGT, emergency drinking water germicidal tablet; gtts, drops; ppm, parts per million.

^*Measure with dropper (1 drop = 0.05 mL) or tuberculin syringe.

^†Povidone-iodine solutions release free iodine in levels adequate for disinfection, but scant data are available.

TABLE 44-9.

Recommendations for Contact Time with Halogenations in the Field

	CONTACT TIME IN MINUTES AT VARIOUS WATER TEMPERATURES
CONCENTRATION OF HALOGEN	5° C (41° F)	15° C (59° F)	30° C (86° F)
2 ppm	240	180	60
4 ppm	180	60	45
8 ppm	60	30	15

NOTE: Data indicate that very cold water requires prolonged contact time with iodine or chlorine to kill Giardia cysts. These contact times have been extended from the usual recommendations in cold water to account for this and for the uncertainty of residual concentration.

Problems

• 1.The taste of the water can be unpleasant when the halogen concentration exceeds 4 to 5 mg/L.
• 2.The potency of some products (tablets, solutions) decreases with time and is affected by prolonged exposure to moisture or heat (tablets) and air (e.g., iodine crystals).
• 3.Liquids are corrosive and can stain clothes and equipment.
• 4.The actual concentration (after halogen demand) is not known.
• 5. Cryptosporidium is highly resistant.

Improving the Taste of Water Disinfected with Halogens

• 1.Add flavoring to the water only after adequate contact time. Iodine will react with sugar additives, thereby reducing the free iodine available for disinfection.
• 2.Use charcoal (GAC) to remove halogen after contact time.
• 3.Reduce the concentration and increase the contact time in clean water. For a small group of people, use a collapsible plastic container to disinfect water with low doses of iodine during the day or overnight.
• 4.
  Iodine and chlorine taste and iodine color can be removed by chemical reduction. In addition, a much higher halogen dose (shorter contact time) can be used if followed by chemical reduction. To remove iodine and chlorine taste and iodine color by chemical reduction:

  • a.
    Add a few granules per liter of ascorbic acid (vitamin C, available in powder or crystal form) or sodium thiosulfate (nontoxic) after the required contact time.
  • b.
    These chemicals reduce iodine or chlorine to iodide or chloride, which has no taste or color.
  • c.
    Ascorbic acid leaves behind a slightly tart taste.
  • d.
    Iodide still has physiologic activity, which means that a person with unstable thyroid disease or known iodine allergy or a pregnant woman should continue to exercise caution.

Superchlorination-Dechlorination

• 1.High doses of chlorine are added to the water in the form of calcium hypochlorite crystals to achieve concentrations of 30 to 200 ppm of free chlorine.
• 2.These extremely high levels are above the margin of safety for field conditions and rapidly kill all bacteria, viruses, and protozoa and could kill Cryptosporidium with overnight contact times.
• 3.After at least 10 to 15 minutes, several drops of 30% hydrogen peroxide solution are added. This reduces hypochlorite to chloride, forming calcium chloride and oxygen.
• 4.The minor disadvantage of a two-step process is offset by excellent taste.
• 5.This is a good technique for highly polluted or cloudy water and for disinfecting large quantities. It is the best technique for storing water on boats or for emergency use. Water is then dechlorinated in needed quantities when ready to use.
• 6.The ingredients can be easily obtained and packaged in small Nalgene bottles (Box 44-8 ; see Table 44-9).

Box 44-8. Improving the Taste of Halogens.

• •Decreased dose; increased contact time
• •Clarification of cloudy water, which decreases amount of halogen needed
• •Removal of halogen
• •Use of granular activated carbon (GAC)
• •Chemical reduction
• •Ascorbic acid
• •Sodium thiosulfate
• •Superchlorination/dechlorination
• •Use of KDF (zinc-copper) brush or media
• •Alternative techniques:
• •Heat
• •Filtration
• •Chlorine dioxide or mixed species (Miox)

▸. MISCELLANEOUS DISINFECTANTS

Mixed Species Disinfection (Miox Purifier)

• 1.Passing a current through a simple brine salt solution generates free available chlorine, as well as other “mixed species” disinfectants that have been demonstrated effective against bacteria, viruses, and bacterial spores.
• 2.The exact composition of the solution is not well delineated because many of the compounds are relatively unstable; however, the resulting solution has greater disinfectant ability than a simple solution of sodium hypochlorite.
• 3. It has even been demonstrated to inactivate Cryptosporidium, suggesting that chlorine dioxide is among the chemicals generated.
• 4.Plan for prolonged contact time, if Cryptosporidium is a strong concern.
• 5.High technology approach will appeal to some.
• 6.Potential for malfunction and battery depletion.
• 7.A new point-of-use commercial product is Miox, marketed by Mountain Safety Research (Seattle, WA) (Box 44-9 ).

Box 44-9. Chlorine Dioxide.

ADVANTAGES

• •Effective against all microorganisms including Cryptosporidium
• •Low doses have no taste or color
• •Portable device now available for individual and small group field use; simple to use
• •More potent than equivalent doses of chlorine
• •Less affected by nitrogenous wastes

DISADVANTAGES

• •Volatile, so do not expose tablets to air and use generated solutions rapidly
• •No persistent residual, so does not prevent recontamination during storage
• •Sensitive to sunlight; keep bottle shaded or in pack during treatment

Relative susceptibility of microorganisms to chlorine dioxide: bacteria > viruses > protozoa.

Chlorine Dioxide

• 1.Chlorine dioxide is capable of inactivating most waterborne pathogens including Cryptosporidium parvum oocysts at practical doses and contact times.
• 2.It is as least as effective a bactericide as chlorine, and in many cases superior.
• 3.It is far superior as a virucide.
• 4.New technology enables cost-effective and portable chlorine dioxide generation in the field. Current products include MicroPUR MP-1, Aquamira, and Miox (Box 44-10 ).

Box 44-10. Ultraviolet Irradiation.

ADVANTAGES

• •Effective against all microorganisms
• •Imparts no taste
• •Portable device now available for individual and small group field use; simple to use
• •Available from sunlight

DISADVANTAGES

• •Requires clear water
• •Does not improve water aesthetics
• •Does not prevent recontamination during storage
• •Expensive
• •Require power source
• •Requires direct sunlight, prolonged exposure; dose low and uncontrolled

Relative susceptibility of microorganisms to ultraviolet: protozoa > bacteria > viruses.

Ultraviolet Light

• 1.In sufficient doses, all waterborne enteric pathogens are inactivated by ultraviolet (UV) radiation.
• 2.Bacteria and protozoan parasites require lower doses than enteric viruses and bacterial spores.
• 3. Giardia and Cryptosporidium are susceptible to practical doses of UV and may be more sensitive because of their relatively large size.
• 4.UV treatment does not require chemicals and does not affect the taste of the water.
• 5.UV works rapidly, and an overdose to the water presents no danger.
• 6.UV light has no residual disinfection power; water may become recontaminated, or regrowth of bacteria may occur.
• 7.Particulate matter can shield microorganisms from UV rays.
• 8.A portable field unit is now available, the SteriPEN. These units require a power source and have great potential.
• 9.
  Another approach uses simple solar disinfection (“SODIS”) technique (see http://www.sodis.ch/).

  • a.
    Transparent bottles (e.g., clear plastic beverage bottles), preferably lying on a dark surface, are exposed to sunlight for a minimum of 4 hours.
  • b.
    Oxygenation induces greater reductions of bacteria, so agitation is recommended before solar treatment in bottles.
  • c.
    Where strong sunshine is available, solar disinfection of drinking water is an effective, low-cost method for improving water quality and may be of particular use in refugee camps and disaster areas (TABLE 44-10, TABLE 44-11, TABLE 44-12 ).

TABLE 44-10.

Summary of Field Water Disinfection Techniques

	BACTERIA	VIRUSES	GIARDIA/AMEBAE	CRYPTOSPORIDIUM	NEMATODES/CERCARIAE
Heat	+	+	+	+	+
Filtration	+	+/−*	+	+	+
Halogens	+	+	+	−	+/−†
Chlorine dioxide	+	+	+	+	+/−†

^*Most filters make no claims for viruses. Reverse osmosis is effective. The General Ecology filtration system claims virus removal.

^†Eggs are not very susceptible to halogens but have very low risk of waterborne transmission.

TABLE 44-11.

Advantages and Disadvantages of Disinfection Techniques

	HEAT	FILTRATION	HALOGENS	CHLORINE DIOXIDE	2-STEP PRCCESS	UV
Availability	Wood can be scarce	Many commercial choices	Many common and specific products	Several new products generate ClO2	Filtration plus halogen, or clarification plus second stage	New portable commercial device; sunlight
Cost	Fuel and stove costs	Moderate expense	Cheap	Depends on method, generally inexpensive	Depends on choice of stages	Commercial device relatively expensive
Effectiveness	Can sterilize or pasteurize	Most filters not reliable for viruses	Cryptosporidium cysts are resistant	All organisms and some parasitic eggs are resistant	Highly effective, should cover all organisms	All organisms
Optimal application	Clear water	Clear or slightly cloudy; turbid water clogs filters rapidly	Clear; need increased dose if cloudy	Clear water, but ClO2 less affected by nitrogenous compounds	May be adapted to any source water	Requires clear water, small volumes
Taste	Does not change taste	Can improve taste, especially if charcoal stage	Tastes worse unless halogen is removed or “neutralized”	Unchanged, may leave some chlorine taste	Depends on sequence and choice of stages; generally improves	Unchanged
Time	Boiling time (minutes)	Filtration time (minutes)	Contact time (minutes to hours)	Prolonged, if need to ensure Cryptosporidium	Combination of time for each stage disinfection	Minutes
Other considerations	Fuel is heavy and bulky	Adds weight and space; requires maintenance to keep adequate flow	Works well for large quantities and for water storage. Some understanding of principles is optimal; damaging if spills or container breaks	More experience and testing would be reassuring; likely to replace iodine for field use	More rational to use halogens first if filter has charcoal stage; C-F is best means of cleaning very turbid water, then followed by halogen, filtration or heat	Sunlight currently for emergency situations or no other methods available; commercial product good for high-quality source water, small group use

C-F, Coagulation-flocculation; UV, ultraviolet.

TABLE 44-12.

Choice of Method for Various Types of Source Water

	“PRISTINE” WILDERNESS	DEVELOPED OR DEVELOPING COUNTRY
	WATER WITH LITTLE HUMAN OR DOMESTIC ANIMAL ACTIVITY	TAP WATER IN DEVELOPING COUNTRY	CLEAR SURFACE WATER NEAR HUMAN AND ANIMAL ACTIVITY*	CLOUDY WATER
Primary concern	Giardia, enteric bacteria	Bacteria, Giardia, small numbers of viruses	All enteric pathogens, including Cryptosporidium	All enteric pathogens plus micro-organisms
Effective methods	Any single-step method†	Any single-step method†	1.Heat 2.Filtration plus halogen (can be done in either order); iodine resin filters (see text) 3.Chlorine dioxide 4.Ultraviolet (commercial product, not sunlight)	C-F followed by second step (heat, filtration or halogen)

C-F, Coagulation-flocculation.

^*Includes agricultural runoff with cattle grazing or sewage treatment effluent from upstream villages or towns.

^†Includes heat, filtration, halogens and chlorine dioxide, ultraviolet.

▸. CHOOSING THE PREFERRED TECHNIQUE

• 1.The best technique for disinfection for either an individual or a group depends on the number of persons, space and weight available, quality of source water, personal taste preferences, and availability of fuel.
• 2.Unfortunately, optimal protection for all situations may require a two-step process of filtration or C-F and halogenation because halogens do not kill Cryptosporidium and filtration misses some viruses.
• 3.Heat works as a one-step process, but it will not improve the taste and look of water if it is cloudy or tastes poor initially.
• 4.An iodine resin, combined with microfiltration to remove resistant cysts, is also a viable one-step process for all situations.

Alpine Camping

• 1.For alpine camping where a high-quality water source is available, heat, mechanical or iodine resin filtration, or a low-dose halogen can be used.
• 2.The only limitation for halogens is Cryptosporidium cysts, but in high-quality pristine surface water the cysts are generally found in insufficient numbers to pose significant risk.
• 3.Heat is limited by fuel supply.
• 4.Filtration has the advantage of imparting no taste and requiring no contact time.

Agricultural Runoff and Discharge from Upstream Towns

• 1.Treat water with agricultural runoff or sewage plant discharge from an upstream town or city with heat or a two-step process of filtration to remove Cryptosporidium, then with a halogen to ensure destruction of all viruses.
• 2.You can also use an iodine resin filter with microfiltration. A filter containing a charcoal element has the added advantage of removing many chemicals such as pesticides.

Surface Water in Undeveloped Countries

• 1.View all surface water in undeveloped countries, even if visually clear, as highly contaminated with enteric pathogens.
• 2.Heat is effective for disinfection, but simple mechanical filtration is not adequate because of the potential for enteric viruses.
• 3.A halogen is reasonable but will miss Cryptosporidium and parasite eggs.
• 4.A two-stage process offers added protection.

Cloudy Water in Developed or Undeveloped Countries

• 1.Pretreat cloudy water in developed or undeveloped countries that does not clear with sedimentation with coagulation-flocculation, and then disinfect with heat or a halogen.
• 2.Note that filters can clog rapidly with silted or cloudy water.

Systems Where Water Will Be Stored

• 1.Halogens have a distinct advantage in locations where the water will be stored for a time such as on a boat or in a home without running water.
• 2.Iodine works for short-term but not prolonged storage because it is a poor algicide.
• 3.
  Note that when only heat or filtration is used before storage, the water can become recontaminated and bacterial regrowth can occur. Superchlorination-dechlorination is particularly useful in this situation because a high level of chlorination can be maintained for a long period.

  • a.
    When ready to use the water, pour it into a smaller container and dechlorinate it.
  • b.
    If another means of chlorination is used, maintain a minimum residual of 3 to 5 mg/L in the water.
• 4.Silver has been approved by the EPA for preservation of stored water.
• 5.On oceangoing vessels where water must be desalinated during the voyage, only reverse-osmosis membrane filters are adequate. Halogens should then be added to the water in the storage tanks (see TABLE 44-10, TABLE 44-11, TABLE 44-12).