Do Water Conservation Measures Help or Hinder Efforts to Reduce Greenhouse Gas Emissions? Findings from a Health Impact Assessment of California Urban Water Conservation

Increasing water demand and decreasing supply bring increased urgency for water conservation to California and other Southwestern states. We conducted a Health Impact Assessment (HIA) of urban water conservation measures that water agencies can adopt in compliance with California Senate Bill x7-7 (also known as "20x2020"), which calls for a 20% reduction of urban water use per water district by 2020.  An important finding from the HIA are the linkages between water use, energy, greenhouse gas emissions, and health.  Because much of the water used in California’s cities is transported hundreds of miles, often over mountains and across deserts, the energy and carbon footprints of this water are especially large.  While reduced water use and increased reliance on recycled water are likely to reduce energy demands and carbon emissions, some alternatives, such as desalination and water transfers, may increase the energy intensity of water and carbon emissions. Another alternative is xeriscaping (ie., landscaping with drought-tolerant plants), a popular water saving strategy that may actually increase greenhouse gas emissions. Most cooling technologies for buildings have inverse relationships between energy and water consumption, saving energy uses more water, saving water uses more energy.  Energy demands for water treatment and recycling can be met and greenhouse gas emissions can be reduced through the use of generators that use methane from wastewater treatments plants, but doing so produces air pollution that can harm local populations.  In a hotter, drier, less stable climate these trade-offs will become more difficult to manage.  Results demonstrate how the link between the energy and water conservation may be related to respiratory disease, mental health, elderly health, and activity-related illnesses. We will discuss options for getting the most out of win-win alternatives and minimizing negative impacts on health when there are unavoidable trade-offs.