WASHINGTON -- The demand for drinking water in cities and the lack of new water sources have spurred water conservation and recycling measures over the last 30 years. Need, coupled with advances in water treatment technology, is motivating a small but growing number of cities to use reclaimed wastewater to supplement drinking water supplies. But, important questions remain regarding the level of treatment, monitoring, and testing needed to ensure public safety.
In its new report, Issues in Potable Water Reuse , a National Research Council committee concluded that reclaimed wastewater can be used to supplement drinking water sources, but only as a last resort and after a thorough health and safety evaluation. Municipalities first must fully assess health impacts from likely contaminants and develop comprehensive systems for monitoring, testing, and treatment. Other water sources and conservation measures also should be tried to the extent practical, before turning to reclaimed wastewater.
Because regulations for safe drinking water were not developed with reclaimed water in mind, they may not be the best standard for testing its quality, the committee said. Reclaimed water may contain sources of contamination that cannot be determined through current testing or treatment processes.
When considering reclaimed wastewater for public water supplies, the public distinguishes between direct and indirect use. Adding highly treated wastewater directly into a water supply without storing it first in a reservoir is not a viable option. Indirect use is viable, however, and that approach was examined by the committee. Indirect use augments the drinking water supply by adding reclaimed treated water first to a lake, reservoir, or underground aquifer. The mixture of natural and reclaimed water is then subjected to normal water treatment before it is distributed as drinking water for the community. Since the 1960s, California's Los Angeles county has operated an indirect-use system in which wastewater, mixed with stormwater and river waters, supplies about 16 percent of total flow into groundwater basins. This mixture then is used as a source for drinking water supplies.
The committee reviewed other reclaimed-water projects currently operating in the United States, including those supplying Northern Virginia, Orange County, Calif., and Phoenix. It also examined feasibility studies made by the cities of San Diego and Tampa. Limited data from projects and studies nationwide show that highly-treated reclaimed wastewater produced drinking water of excellent quality, and that no obvious health effects have been found in animal tests or in communities where reclaimed water has been used. These results are insufficient, however, and more information is needed, the report says.
Given health and safety concerns, the committee identified key priorities for water agencies that add treated wastewater to their systems, or are considering doing so:
Copies of Issues in Potable Reuse: The Viability of Augmenting Drinking-Water Supplies with Reclaimed Water are available from the National Academy Press for $34.95 (prepaid) plus shipping charges of $4.00; tel. (202)334-3313 or (800)624-6242.
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