Reclaimed wastewater can augment municipal drinking water supplies but uncertainties must be addressed

April 1998

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:

• Evaluate the potential health effects from possible contaminants. All major sources of household, industrial, and agricultural chemical contaminants in reclaimed water should be documented and removed based on existing federal clean water standards. Since it is unclear whether or not highly treated wastewater contains harmful levels of byproducts from disinfection processes such as chlorination. This issue should be addressed by the research community. The Environmental Protection Agency should sponsor a study to develop methods for better detection of new pathogens. Most outbreaks of waterborne disease in the United States are caused by parasites and viruses, yet few drinking water systems monitor for the full range of such pathogens.

• Assess the health risks of drinking reclaimed water. After reviewing the few studies that have examined the health implications of drinking reclaimed water, the committee said that different approaches are needed to test the safety of reclaimed water. Conventional toxicology tests developed by the food and drug industries are not appropriate for evaluating the risks from complex chemical mixtures that can be found in reclaimed water. Alternative studies, such as tests using fish in source water, should be made to provide a broader range of data about possible harmful effects to living organisms. Research also is needed on the level of viruses and parasites in all waters and the effectiveness of both conventional and advanced water treatment processes in removing these pathogens. The federal government should undertake population studies that compare the disease rates over time among individuals exposed to reclaimed water to the disease rates among individuals who use a different water source.

• Monitor the reliability and operation of water treatment systems. There are two essential keys to the safe, reliable operation of a reclaimed-water treatment system: good design that provides redundant safety measures to prevent contamination, and monitoring systems that detect variations in water quality and system performance. Other measures should be implemented as well. Since waterborne viruses. bacteria, and parasites pose the greatest threat to public safety, water treatment procedures for removing them should necessarily be the most stringent. Communities using reclaimed water should implement well-coordinated, public health surveillance systems to document and provide early warning of any adverse health effects associated with the ingestion of reclaimed water.

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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