Quantifying water overconsumption using a new water supply sustainability indicator

Communities around the globe are experiencing great difficulty in constraining their water consumption within the limits of available, renewable freshwater supplies. When water consumed from freshwater supplies exceeds natural replenishment from snowmelt, rainfall, or aquifer recharge, freshwater sources can become depleted to the point that water shortages emerge with serious consequences for economies, human and ecosystem health, and social disruption. We describe a quantitative approach—called the “Indicator of Water Supply Sustainability" or IWSS – for assessing trends in the freshwater sources being utilized for water supply in cities, industries, power plants, and on farms, and demonstrate its use in six river basins in the western United States. Our integrated assessment approach considers trends in all affected freshwater sources including rivers, lakes, reservoirs, and aquifers, which can serve as a means for assessing water-supply sustainability and as a warning signal that water security may be jeopardized if declining trends exist and persist. Importantly, trends in freshwater sources are based on measured conditions using water data that can be accessed and evaluated for many regions around the world.