A novel approach to quantify indirect ingestion of recycled water: Improving the evidence base for water guidelines

Stormwater and treated wastewater can contain infectious pathogens. The Australian Guidelines for Water Recycling (AGWR) require that these are removed during recycling, and that recycling processes pass “Quantitative Microbial Risk Assessments” (QMRA). The problem is that these QMRA’s are often based on estimates. This research further developed methods (begun in WaterRA project 3002) to generate real-world measurements and data relevant to firefighters and domestic users because there are concerns that small amounts of recycled non-potable water might be inadvertently ingested. To test this, a harmless chemical, cyanuric acid, was added to safe water, then twenty-six volunteers used it, and a domestic high-pressure sprayer, to clean a full-sized model car for 10 minutes. The volunteers then collected their own urine for the next 24h because if this test-water is ingested, the cyanuric acid can be measured in the urine. From this it was discovered that the volunteers ‘drank’ an average of 0.13mL. This led to the conclusion that the conservative estimates in the AGWR currently protect domestic non-potable recycled water users, but that prolonged and/or high intensity occupational use of high-pressure sprays should be investigated further.