FEASIBILITY OF HARVESTED RAINWATER AS A SUPPLEMENTAL IRRIGATION WATER SOURCE ON URBAN FARMS

Abstract

My dissertation investigated the feasibility of using harvested rainwater as a supplemental irrigation water source on urban farms. My objectives were to 1) evaluate the quality of harvested rainwater and the validity of water treatment technologies on urban farms, 2) develop a University of Maryland Extension publication to help urban farmers harvest rainwater, and 3) evaluate harvested rainwater as irrigation water according to the U.S. Food and Drug Administration (FDA) Food Safety Modernization Act (FSMA) Final Rule on Pre-Harvest Agricultural Water. Between April 2024 and June 2025, six experiments were conducted to collect, treat, and use harvested rainwater to irrigate produce. Water, produce, and soil samples were analyzed for fecal indicator bacteria, foodborne pathogens, and physicochemical properties. Harvested rainwater treated with peroxyacetic acid and zero-valent iron and sand filtration had lower levels of fecal indicator bacteria compared to untreated harvested rainwater. Peroxyacetic acid effectively reduced L. monocytogenes below the limit of detection in the harvested rainwater. E. coli and physicochemical testing results indicated that irrigating with treated harvested rainwater would have minimal impact on produce and soil when compared to municipal water. Overall, our results pointed to the need for urban farmers to treat their harvested rainwater before using it to irrigate fresh produce. An Extension publication was developed to provide instructions for capturing rainwater from a high tunnel. Cost estimates, rainwater collection potential, and food safety concerns were all addressed to improve confidence in harvested rainwater as an irrigation source. Irrigating with harvested rainwater was also explored through the lens of the U.S. FDA FSMA Final Rule on Pre-Harvest Agricultural Water. By applying decision-making tools developed by the U.S. FDA to scenarios where harvested rainwater is used to irrigate fresh produce, treated harvested rainwater was determined to be the optimal route for minimizing food safety concerns compared to untreated harvested rainwater. My dissertation findings address important knowledge gaps in reducing risk when irrigating fresh produce with harvested rainwater. Treating harvested rainwater could address concerns about water quality and food safety. By implementing rainwater harvesting, urban farms could improve their climate resiliency and expand their ability to feed their communities.