UC Irvine

Sustainable Urban Water Management (SUWM), a new approach to manage stormwater as a water resource instead of nuisance, has the potential to supplement the diminishing traditional water supplies as well as reducing surface water pollution from storm runoff. Uncertainties of public health risks represent one of the main barriers for the smooth transition to SUWM approach as urban stormwater is known to be highly variable in water quality and is less studied than the conventional water supplies. My research is aimed at improving our state-of-knowledge for the public health risks associated with the SUWM practices. Using the Quantitative Microbial Risk Assessment (QMRA) framework as my main research tool, I investigated the risk implications of three SUWM scenarios: 1) rainwater harvesting, 2) stormwater harvesting, and 3) discharging stormwater into recreational water. As household-level rainwater harvesting is the most readily implementable SUWM approach, I first investigated the public health risks associated with using the rooftop harvested rainwater for household produce irrigation—a reasonable scenario considering the relatively clean water quality of rainwater. My result showed that the risk associated with consuming produce irrigated by harvested rainwater exceeded the EPA’s benchmark for safe drinking water, but is still at least ten-fold lower than when reclaimed water is used for the same purpose. To investigate the risks associated with capturing, treating, and reusing urban stormwater collected from urban developments, I examined three non-potable household applications: 1) toilet-flushing, 2) showering, and 3) foodcrop irrigation. My results showed that harvested stormwater is only safe for toilet-flushing under the circumstances considered. However, interpretations of the risks also differ depending on the risk benchmark used for comparison. In my final case study, I adopted a new contamination source apportionment QMRA method to investigate the recreational health risks associated with discharging stormwater into a popular recreational beach. My results showed that sewage contamination of urban stormwater is the governing factor for elevated risks in the water. However, the risk levels are within the acceptable risk set by the U.S. EPA in most of the cases in spite of the violation of water quality standard due to contribution of fecal bacteria from non-human sources. The overall finding of my research demonstrated that the QMRA is a powerful tool to provide a scientific basis for SUWM decisions. The risk outcomes can be used to set the appropriate public health risk management guidelines and water legislation that are necessary for the progress of SUWM practices.