Use of reclaimed wastewater in municipal drinking-water supplies.

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. Coupled with advances in water treatment technology, this need is motivating some cities to supplement drinking-water supplies with reclaimed wastewater. But important questions remain about the level of treatment, monitoring, and testing needed to ensure public safety.

Issues in Potable Water Reuse, a new report from NRC, concludes that reclaimed wastewater can supplement drinking-water sources, but only as a last resort and only after a thorough health and safety evaluation. Municipalities must fully assess health impacts from likely contaminants and develop comprehensive systems for monitoring, testing, and treatment.

Uncertainties Must Be Addressed

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 Reclaimed water may be contaminated in ways that cannot be determined through current testing or treatment processes.

The report distinguishes between direct and indirect use of reclaimed wastewater. 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 the report examines that approach. 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, Los Angeles County, California, has operated an indirect-use system in which wastewater, mixed with storm water and river water, supplies about 16 percent of total flow into groundwater basins. This mixture then is used as a source for drinking water.

Other reclaimed-water projects in the United States supply northern Virginia; Orange County, California; and Phoenix. Feasibility studies have been conducted by the cities of San Diego and Tampa. Limited data from projects and studies nationwide show that highly treated reclaimed wastewater has 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.

Given health and safety concerns, the report identifies three priorities for water agencies that add treated wastewater to their systems or are considering doing so.

Evaluation of Potential Health Effects of Possible Contaminants

All major household, industrial, and agricultural chemical contaminants in reclaimed water should be documented and removed according to existing federal clean-water standards. It is unclear whether highly treated wastewater contains harmful levels of byproducts from disinfection processes such as chlorination, and this issue should be addressed by the research community. U.S. EPA 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.

Assessment of the Health Risks of Drinking 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 with fish in source water, should be undertaken to provide a broader range of data about possible harmful effects. Research also is needed on the level of viruses and parasites in all waters and the effectiveness both of conventional and of advanced water treatment processes in removing these pathogens. The federal government should undertake population studies that compare the disease rates over time.

Monitoring of the Reliability and Operation of Water Treatment Systems

Safe, reliable operation of a reclaimed-water treatment system depends on two factors: 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 that use 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.

Further Information

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 plus shipping. Orders can be placed by telephone at [phone] or [phone].