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Human Health Impact of Cross-Connections in Non-Potable Reuse Systems
Citation:
Schoen, M., M. Jahne, AND J. Garland. Human Health Impact of Cross-Connections in Non-Potable Reuse Systems. WATER. MDPI, Basel, Switzerland, 10(10):1352, (2018). https://doi.org/10.3390/w10101352
Impact/Purpose:
There is growing interest across the United States in onsite non-potable water systems (ONWS) to sustainably manage water. These systems collect various sources of water (e.g., greywater and wastewater) and treat it locally for both indoor and outdoor uses (e.g., toilet flushing and irrigation). Example domestic systems include the Solaire residential building in New York City and the Pimpama-Coomera residential district in Australia. The health risk from exposure to enteric pathogens from designated uses of ONWS following risk-based treatment requirements is considered acceptable (i.e., less than the selected annual benchmark). However, the health impact from unintended exposure events in domestic (or office) ONWS, such as cross-connection contamination events or accidental ingestion, remains uncharacterized in scientific literature, with the exception of one well-studied event in the Netherlands. This work explores the possible health impact of cross-connections in domestic (or office) ONWS, defined here as intrusion of lesser quality water into a water system, based on reported events from the literature as well as using quantitative microbial risk assessment (QMRA). Results will be useful guidelines for States that may require the reporting of contamination events or testing for unprotected cross-connections in ONWS.
Description:
We used quantitative microbial risk assessment (QMRA) to estimate the microbial risks from two contamination pathways in onsite non-potable water systems (ONWS): contamination of potable water by (treated) reclaimed, non-potable water and contamination of reclaimed, non-potable water by wastewater or greywater. A range of system sizes, event durations, fraction of users exposed, and intrusion dilutions were considered (chlorine residual disinfection was not included). The predicted annual microbial infection risk from domestic, non-potable reuse remained below the selected benchmark given isolated, short-duration intrusion (i.e., 5-day) events of reclaimed water in potable water. Whereas, intrusions of wastewater into reclaimed, non-potable water resulted in unacceptable annual risk without large dilutions or pathogen inactivation. We predicted that 1 user out of 10,000 could be exposed to a 5-day contamination event of undiluted wastewater in the reclaimed, non-potable water system each year to meet the annual benchmark risk of 10−4 infections per person per year; whereas, 1 user out of 1000 could be exposed to a 5-day contamination event of undiluted reclaimed water in the potable water each year. Overall, the predicted annual risks support the use of previously derived non-potable reuse treatment requirements for a variety of ONWS sizes and support the prioritization of protective measures to prevent the intrusion of wastewater into domestic ONWS.
