Wastewater agencies produce highly treated water that is increasingly being reused as a water supply. While it’s still only a small portion of overall water use, the use of recycled water has nearly tripled since the 1980s―and is continuing to rise as water agencies seek to meet the demands of a growing population and improve the resilience of their water supplies.
Recycled water production is closely related to water use and wastewater management. It also directly influences flows for ecosystems and downstream water users in some watersheds. As its use expands, weighing the trade-offs involved will help avoid conflict. Meeting current and future demands requires careful consideration of several issues, including the impact of water use on wastewater management, changing types of demand for recycled water, and the needs of ecosystems and downstream users.
Recycled water production is affected by reductions in water use. In other words, recycled water is not completely “drought proof.” The drought of 2012‒16 provides a clear example of this. The rapid reduction of urban indoor water use in this period resulted in a reduced quantity and quality of wastewater for most of the state’s wastewater agencies. In a survey conducted by the PPIC Water Policy Center, just over 40% of wastewater agencies that recycle wastewater reported that their ability to produce recycled water was impaired during the drought. The long-term efficiency of water use and related declines in wastewater quality may also affect recycled water production in the future. For example, as households become more water-efficient, the wastewater they discharge to sewers can have higher concentrations of salts, which are not removed in most treatment processes. Saltier water may not be suitable for outdoor irrigation of golf courses or lawns—common uses of recycled water. If this issue grows in severity, agencies may be forced to incorporate desalination into wastewater treatment, which is likely to add cost and complexity.
Demand for recycled water is growing and changing. Recycled water is increasingly being used in urban areas for public landscape irrigation, golf courses, industrial cooling, and groundwater recharge. Replenishing sources of drinking water is the biggest growth opportunity for water recyclers. New state rules allowing replenishment of groundwater and surface water storage with recycled water—and eventually the direct connection of recycled water to drinking water infrastructure—will create opportunities for recyclers to cost-effectively meet growing demands well into the future. This will require close coordination between water suppliers and wastewater agencies. Some wastewater agencies will also need to increase their treatment capacity to meet the higher water quality standards required for potable reuse.
Expanding use of recycled water may reduce flows of treated wastewater in rivers, streams, and estuaries. Treated wastewater is an important water source for some ecosystems and downstream water users. Watersheds where wastewater makes up a significant amount of the flow that supports ecosystems and downstream users are especially vulnerable to conflict. For example, a proposal to increase the use of recycled water in Coachella Valley would decrease flows to the already shrinking and vulnerable Salton Sea. Managing recycled water so that it avoids harm to ecosystems and downstream users will require additional collaboration and thoughtful planning.
Closer coordination between wastewater agencies and water suppliers can help minimize impacts from changing patterns of water use on wastewater quantity and quality. Regional planning can also help agencies make smart recycled-water investments that take advantage of opportunities to more directly replenish drinking water supplies. New projects should be based on a careful consideration of local demands and costs, and also how well the investment fits into the overall regional supply of water for both human and environmental uses. Taking such steps now can help water managers in this growing sector make the most of this once-maligned resource.