Risk-Based Review of California’s Water-Recycling Criteria for Agricultural Irrigation

AbstractCalifornia currently recycles treated wastewater at a volume of approximately 8.0×108  m3 of water per year, with a potential to recycle an additional 1.9×109  m3 per year. A key challenge in promoting the expansion of water recycling for agricultural purposes was addressing the perceived concern about whether recycled water produced in conformance with California law is protective of public health. The California Department of Public Health (CDPH) established an expert panel to consider the concern. The panel found, based on quantitative microbial risk assessment (QMRA), that the annualized median risks of infection for full tertiary treatment ranges from 10−8 to 10−4 (for human enteric viruses Cryptosporidium parvum and Giardia lamblia, and Escherichia coli O157:H7) based on the assumption of daily exposure. The panel found that risk estimates are consistent with previous CDPH estimates and concluded that current agricultural water recycling regulations do not measurably increase public health risk.