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reliability evaluation." Critics of indirect potable reuse have focused on language in the report identifying indirect potable reuse as, "an option of last resort," to be used only when olher options are, "technically or economically infeasible." INDIRECT POTABLE REUSE How recycled water is used determines the level of treatment. The greater the potential for human contact, the stricter the criteria. For water to be fit for human consumption, it must meet stringent state and federal standards. Since 1962, WRD has been using recycled water to recharge overdrafted underground basins that serve as a potable supply for residential areas in the Los Angeles area. The district spreads the water above deep aquifers and as the treated water percolates through the soil, it is further filtered. Since the mid-1990s, approximately 50,000 acre-feet of re- cycled water has been spread annually, making WRD the largest regu- lated reclaimed water user in the state. Eventu- ally, WRD plans to recycle more Ihan 100,000 acre- feet of water per year. According to a 1984 health effects study con- ducted by the Los Ange- les County Sanitation Districts and the UCLA School of Public Health of WRD's groundwater replenish- ment project at Whittier Narrows (affecting 900,000 people), no detectable impact on human health was found. A 1991 update of the study by the RAND Corporation supported the 1984 findings and found, "rates of cancer, mortality, and infectious disease were similar in bolh the area of Los Angeles County receiving some reclaimed water and a control area not receiving reclaimed water." Mixing advanced treated recycled water into drink- ing water supplies - indirect potable reuse - has raised some health concerns about unknown patho- gens (particularly viruses) or unidentified chemical constituents because of their small size. A national report assessing possible health implications of indirect potable reuse of recycled water to augment drinking water sources was completed in 1998. The report, Issues in Potable Reuse: The Viability 01 Augmenting Drinking Water Supplies Wilh Reclaimed Water, by the National Research Council, concluded that, "planned, indirect potable reuse may be practicable where there is a careful, thorough, project-specific assessment, including contaminant monitoring, health and safety testing and syslem In essence, the report admits the limitations of current water testing and standards and as a result, does not attempt to compare recycled water quality with a similar potable water source. The report states that federal SDWA standards are aimed at water obtained from conventional, relatively uncontaminated sources of water and were not intended to apply to recycled water. The report calls for in- direct potable reuse standards to be more stringent than those applied 10 convenlional drinking water supplies. It adds that although the epide- miological and toxicological data on Ihe health risks of microbial pathogens or un- known chemical mixtures in recycled water suggest that advance treated water is safe, the information is sparse and insufficient. The report acknowledges, however, that similar concerns exist over the current testing of potable water from conventional waler sources and that given the best current information available, "these uncertainties are not adequate reason for rejecling indirect potable reuse." ., Further exploration into whether or not indirect potable use meets SDWA standards also was made by DHS and DWR in a 1996 guidance document entitled Indirect Potable Reuse 01 Advanced Treated Reclaimed Water by Surface Water Augmentation in California. This framework on using treated water to increase potable supplies recommends several criteria be met before allowing indirect potable use of recycled water for sutiace water augmentation. The recommendations include using the best available technology in an advanced wastewater treatment plant such as membranes and ozone; meeting drinking water standards; carefully monitor- ing the project; and ensuring "appropriate retention time" for the repurified water in a reservoir in order to respond to any treatment failures before treating it one more time in a drinking water treatment plant and blending it with the existing supply. 9