Table 2.

Urban water cycle.

Availability and quality	Impacts	-Water scarcity: almost 65% of the population has access to less than 1,000 m3/inhabitant/year of water (Fig. 2) [83]. -Discharge volumes in the Maipo Basin (the principal supplier of potable water for the Santiago metropolitan area) are estimated to decrease by up to 40% in the future [84]. -Droughts impact water quality [85,86]. -High turbidity events impact the operation of the drinking water supply systems [86,87]. -High concentrations of metals and metalloids in rivers of northern-central zones [88] and groundwaters [21].
	Causes	-Climate change: lack of precipitation and drought [89]. -Intensive use of water by mining and agriculture activities [90]. -Climate change: warm storms in the Maipo River [91] causing high turbidity events. -Geogenic metal enrichments in addition to anthropogenic activities in the northern and central zones of Chile [92].
	Current plans for action	-National Strategic Plan for Disaster Risk Reduction in the Water Sector 2020–2030 [93]. -Framework law of climate change: establish water balance and projections, information on quantity, quality, infrastructure, and institutions that intervene in the decision-making process regarding water resources and propose a set of actions to safeguard water security [37]. -Construction of reservoirs to increase the autonomy of water production systems and reduce the impact of turbidity events [94]. -Expansion of the monitoring network, promotion of scientific research, and early warning systems [94]. -More comprehensive surveillance programs for ambient water quality standards [21]. -Establishment of regulations and standards for the collection, reuse, and disposal of greywater [95].
Distribution and consumption of drinking water	Impacts	-Total urban water production increased by 40% between 1999 and 2020, up to 1,787 million m3 per year (Fig. 3) [86,96]. -There is a national average of 33.4% of non-revenue water in 2020 [86]. -Water leakages in the distribution system are estimated to account for 74% of non-revenue water [97]. -Access to drinking water, sewage, and wastewater treatment in urban areas in 2020 reached 99.9%, 97.3%, and 97.3% [86]. -Water consumption per capita in Chile: 17.4 m3/client/month in 2020 (i.e. approximately 161 L/day/person) (Fig. 3) [86].
	Causes	-Urban population growth [98]. -Inefficient water markets due to lack of complete information, poorly flexible distribution systems, high transaction costs [99], and fragmented governance of water resources [100].
	Current plans for action	-Water leakage control strategies: pressure management [101], night flow analysis in individual District Metering Areas (DMAs) [102]. -Incorporate network monitoring systems and increase the replacement of obsolete infrastructure [103].
Wastewater treatment	Impacts	-Alteration of marine ecosystem functioning: effects on the biochemical composition of sediments, production of organic enrichments, which later degradation lead to lower oxygen concentrations and hypoxia [104]. -Pharmaceuticals and personal care products found in effluents from wastewater treatment plants involve endocrine disruption effects on freshwater fish [105]. -Highly energy-intensive activated sludge technology with important volumes of sewage sludge [106,107].
	Causes	-Excessive discharge of nutrients (nitrogen and phosphorus) to water bodies [21]. -Marine outfalls collect 11% of wastewaters: 33 of the 301 treatment systems include neither biological nor chemical processes [86]. -Tertiary treatment is not performed for nutrient removal in wastewater treatment plants [21]. -The lack of secondary environmental standards (i.e. regulating ambient pollutant concentration) in Chilean water bodies, similar to Total Maximum Daily Loads (TMDL) [108]. -Plants are not designed to remove pollutants such as pharmaceuticals and personal care products [105]. -Use of energy-intensive technology in various stages of the treatment process [109,110], in an urban water cycle not optimized in terms of energy efficiency [111].
	Current plans for action	-Development of secondary environmental standards: Five of the 101 watersheds have secondary environmental standards [112]. -Modification of the Supreme Decree Nº90 standards for liquid waste discharges into marine and continental surface waters [113]. -Define watershed-specific ambient water quality standards and more stringent discharge standards for treated wastewaters [21].
Stormwater management	Impacts	-Large stormwater volumes and discharges cause urban flooding and fluvial ecosystem deterioration [114,115]. -Degradation of the quality of water bodies receiving stormwaters [116].
	Causes	-The replacement of the vegetation cover with impervious surfaces [117]. -The occupation and poor management of floodplains [118]. -Urban areas as nonpoint sources of metals, oxygen-demanding substances, and suspended solids transported in stormwaters [116].
	Current plans for action	-The urban drainage manual provides planning strategies, designing tools, and standards for stormwater control (i.e. conveyance, infiltration, and storage) [119]. -The sustainable urban drainage guide for southern Chile provides information about natural drainage systems, including green infrastructures, the national regulatory framework, and planning strategies for their implementation [120].