Arizona rooftop harvested rainwater: How clean is it?

The United Nations Sustainable Development progress report states that 2.3 billion people live in water-stressed countries and that water scarcity could force migration for more than 700 million people by 2030 (United Nations, 2021). As climate change worsens water scarcity (Schewe et al., 2014), the U.S. and even Arizonans will become more reliant on alternative sources of water (Pearson et al., 2015; Tamaddun et al., 2018), such as rooftop harvested rainwater (RHRW). In Arizona (AZ), the average resident uses 120 gallons (454.2 L) of water per day; this municipal use contributes to 20% of the state’s water budget. In comparison, 78% is allocated for agricultural and 1% for industrial uses (Arizona Department of Water Resources, n.d.). Up to 70% of residential water is used for outdoor activities such as gardening and filling swimming pools, with that number increasing during the warmer months (Arizona Department of Water Resources, n.d.).