Water resource managers use a combination of approaches to manage water sustainably in conditions of drought and scarcity. Common approaches include:

• demand management (water conservation and efficiency)
• reclamation and reuse of wastewater
• acquisition of a portfolio of physically and legally distinct water supplies
• use of renewable surface water supplies in lieu of depletion of fossil groundwater supplies
• development of additional reservoirs or rehabilitation of existing reservoirs
• aquifer replenishment and recharge
• stormwater capture
• crop rotation and crop fallowing
• transfer of water from its original purpose to a preferred one
• leases, trades, and exchanges of existing water rights
• desalination of brackish groundwater or seawater
• rehabilitation and replacement of aging water infrastructure

This section discusses four of the prominent technological approaches to water management: demand management, water capture and reuse (including stormwater capture), aquifer replenishment and recharge, and desalination. The role of the judiciary in water management under scarcity is also discussed.

1. Demand management

Water efficiency is defined as the use of technology to reduce the use of water without changing behavior. Farmers can use high-efficiency drip irrigation to directly feed water to a plant’s roots instead of spreading it widely over the ground surface via a sprinkler system. Industries can opt to use air-cooled rather than water-cooled systems. And municipalities and homes can switch to systems like low-flush toilets and low-head showers. The federal labelling program driving most municipal and residential water efficiency programs is EPA WaterSense [23].

Water conservation aims to reduce the consumption of water by changing behavior. A major water conservation effort in urban areas is educating consumers on the contribution of leaks to water waste. Another effort aims to minimize outdoor water use by encouraging homeowners to select garden vegetation that requires little or no irrigation (xeriscaping). Agricultural water use can be similarly mitigated by effective choice of low-water and drought-resistant crop species.

2. Capture and reuse

Water reuse has become a key aspect of water management programs in water-stressed regions. Unplanned reuse (also known as de facto reuse) happens when a percentage of a water supply is composed of outflow from an upstream system. De facto reuse is common, especially in arid areas. In fact, over 80 percent of all large cities that source their water from surface water are subject to some level of de facto reuse [24]. Planned water reuse can be put towards a variety of goals, including aquifer recharge. (Pumping water from these aquifers as a municipal water source is known as indirect potable reuse.) Water in these systems must be “fit-for-purpose,” meaning that it must be treated to a sufficiently pure level to not harm humans directly or indirectly exposed to it. In other words, water that comes into direct contact with humans, such as water used in irrigated agriculture, will be treated to a much higher standard than water used in an indirect situation, such as flushing a toilet. Water reused in this fashion is sometimes known as a “purple pipe system”, after the authorized plumbing code for reused water. State and local laws may hold treatment of reused water to a higher standard than federal regulations [25]. For a discussion of water treatment for reused water under the Clean Water Act, see the module on Water Quality.

Stormwater capture and infiltration repurposes runoff, particularly in urban areas, that would otherwise contribute to localized flooding. In cities, an increase in the amount of paved surface leads to less water being absorbed into the ground or taken up by plants and trees and returned to the atmosphere via evapotranspiration. Green stormwater infrastructure is designed to return cities to a more natural hydrology, using engineered systems, planned green space, and native landscaping to capture and treat stormwater at its source. Green infrastructure can be used to infiltrate stormwater to replenish local aquifers. Certain types of green infrastructure like rain barrels and blue roofs can also be used to collect stormwater for later reuse on-site [26].

3. Aquifer replenishment and recharge

Managed Aquifer Recharge (MAR) is a suite of technologies and management strategies that replenish an aquifer using surface or underground recharge techniques. Short- and long-term studies of MAR facilities in California’s Central Valley indicate that MAR can be a valuable tool in offsetting the effects of aquifer depletion [27].

Surface water can be diverted to naturally infiltrating river channels during low-flow seasons or to artificial ponds and streams known as spreading grounds located in fast-draining soil [28]. In arid or semi-arid areas, temporary check dams on ephemeral streams can be used to slow down water flowing in the streams during the rainy season, reducing the risk of flash flooding and improving aquifer recharge [29]. Aquifers can also be recharged using deep-injection wells with alternative water sources such as captured stormwater or treated wastewater [28].

Source quality is important, particularly for MAR using deep-injection, as no additional treatment of the water takes place through filtration through the soil. Captured stormwater can be of variable water quality (unless pretreated), while the quality of wastewater effluent for deep-injection varies by state. Some states allow the injection of raw (untreated) wastewater effluent into groundwater. The water quality issues associated with MAR include groundwater (and potentially connected surface water) contamination with pathogens, nutrients, and disinfection byproducts and the mobilization of heavy metals and radionuclides into groundwater [30].

MAR works well in both confined and unconfined aquifers, though it is important for the aquifer to have an impermeable confining bottom layer to prevent seepage of recharged water into deeper, inaccessible strata [28]. For more information on aquifer hydrology, see our groundwater module.

4. Desalination

Desalination is the process of removing excess salt from seawater or brackish groundwater to make it fit for domestic, agricultural, or industrial use. The most common large-scale desalination process is reverse osmosis (also used in tertiary wastewater treatment). In osmosis, two water-based solutions separated by a permeable membrane will naturally diffuse so that the concentration of solutes (dissolved substance) is equal on both sides of the membrane. Reverse osmosis uses energy to reverse this natural diffusion, creating a pressure gradient that forces pure water to one side of the membrane and excessively salty brine to the other [31].

Modern membrane technology has increased the efficiency of this practice. Reverse osmosis membranes have published rejection rates of only 99.8 percent, meaning that only 0.2 percent of the salts in the original feedwater pass through the membrane into the finished product. In practice, the rejection ratio depends on a variety of factors, including temperature and the types of salt present in the water [32]. 

The energy required for reverse osmosis is high. The osmotic pressure required to desalinate seawater is between 800–1000 psi; the cost to run the pumps needed to sustain these pressures accounts for 25–40 percent of the overall cost of water. Furthermore, the upfront capital costs to build a reverse osmosis desalination plant can amount to hundreds of millions of dollars [33].

Reverse osmosis also produces hypersaline brine as a byproduct. This brine—which is two to three times saltier than seawater and 25 percent warmer—is typically discharged directly into the ocean. Benthic fauna, plankton, fish, and seagrasses can suffer negative effects associated with osmotic stress and increased temperatures at distances several hundred meters from the discharge outfall [34].

The impact of judicial decisions on managing water sustainability

Judicial decisions impact sustainable water management, particularly in the arid West. To manage water rights effectively, water resources managers need to have certainty in water rights. Adjudications, court interpretations, and water rights settlements create the certainty necessary for investment in sustainable water management. Certainty in property rights to water—rights that are exclusive, transferrable, and enforceable—allow for innovative partnerships, transfers, leases, and exchanges that enable water to flow to its highest and best purpose under conditions of scarcity. For example, the cities of the Phoenix metropolitan area have made enormous investments in the reclamation and reuse of wastewater because of the Arizona Supreme Court’s 1989 ruling in Arizona Public Service v. Long that cities have the right to sell reclaimed wastewater or put it to other beneficial uses (APS v. Long, 1989). Without this certainty, cities would not have invested the huge sums necessary to develop this source as a significant part of their water supply portfolios.

Conflicts over drought and water scarcity are often resolved by achieving a reduction in water use in one or more of the relevant parties, either voluntarily through transfers, sales, leases, exchanges, incentives to conserve, and quid-pro-quo trades, or involuntarily through court injunctions. Where settlements involving these tools cannot be achieved, the certainty provided by judicial decisions allows additional water resource development and planning to take place.

[23] U.S. Environmental Protection Agency, “Water Efficiency for Water Suppliers,” Feb. 25, 2022. [Online]. Available: https://www.epa.gov/sustainable-water-infrastructure/water-efficiency-water-suppliers. [Accessed June 30, 2022].

[24] S. Turner, et al., “Comparison of potential drinking water source contamination across one hundred U.S. cities,” Nature Communication, vol. 12, p. 7254, 2021.

[25] U.S. Environmental Protection Agency, “Basic Information about Water Reuse,” June 13, 2022. [Online]. Available: https://www.epa.gov/waterreuse/basic-information-about-water-reuse. [Accessed June 30, 2022].

[26] F. Ahammed, “A review of water-sensitive urban design technologies and practices for sustainable stormwater management,” Sustainable Water Resources Management, vol. 3, p. 269–282, 2017.

[27] D. Wendt, et al., “Managed aquifer recharge as a drought mitigation strategy in heavily-stressed aquifers,” Environmental Research Letters, vol. 16, p. 014046, 2021.

[28] K. Luxom, “Managed Aquifer Recharge,” American Geosciences Institute, Sept. 25, 2017. [Online]. Available: https://www.americangeosciences.org/geoscience-currents/managed-aquifer-recharge. [Accessed July 5, 2022].

[29] H. Djuma, et al., “The Impact of a Check Dam on Groundwater Recharge and Sedimentation in an Ephemeral Stream,” Water, vol. 9, no. 10, p. 813, 2017.

[30] U.S. Environmental Protection Agency, “Aquifer Recharge and Aquifer Storage and Recovery,” Nov. 16, 2021. [Online]. Available: https://www.epa.gov/uic/aquifer-recharge-and-aquifer-storage-and-recovery. [Accessed July 5, 2022].

[31] U.S. Food and Drug Administration, “Reverse Osmosis,” in Inspection Technical Guides, Washington, D.C., USFDA, 1987.

[32] H. Fravel, “Understanding Salt Passage Vs. Salt Rejection In Reverse Osmosis Systems,” Water Online, Aug. 29, 2014. [Online]. Available: https://www.wateronline.com/doc/understanding-salt-passage-vs-salt-rejection-in-reverse-osmosis-systems-0001. [Accessed July 5, 2022].

[33] U.S. Department of Energy, “Desalination,” in Powering the Blue Economy: Exploring Opportunities for Marine Renewable Energy in Maritime Markets, Washington, D.C., USDOE, 2019, pp. 86–98.

[34] S. Bianchelli, et al., “Impact of hypersaline brines on benthic meio- and macrofaunal assemblages: A comparison from two desalination plants of the Mediterranean Sea,” Desalination, vol. 532, p. 115756, 2022.