Understanding the Limits of Residential Water Conservation through Generalized, Basin-Scale System Dynamics

Population growth and climate change have strained existing water supplies requiring municipalities to shift towards demand management strategies to ensure reliable water provisions. Particularly in the residential sector, water conservation measures and incentives have been utilized to reduce demand during short-term shortages. As water conservation programs are now being commonly utilized as a way to ensure enough water will be available for continued growth, the impacts on a basin-wide scale have yet to be established. By changing the relative water demand for indoor and outdoor uses within a municipality, the amount of water being consumed can thereby reduce the effluent available for downstream communities. This research investigates how the timing of water conservation, water conservation strategy, and population growth impact water availability in a shared basin. A generalized system dynamics model reflecting typical residential water use and availability patterns similar to the southwest United States was utilized. We found that when upstream municipalities focus their initial reductions on non-consumptive demands, downstream municipalities reliant on upstream return flow have to increase their conservation rate to meet demands and maintain population growth. When most of the basin's population is in upstream municipalities, the more influence their change in water use has on downstream water availability. Therefore, consumptive conservation should be the priority of basin-wide conservation programs to ensure return flow is sufficient to satisfy the demands of downstream municipalities.