Competing incentives and poor water quality in private water systems

Abstract:

Private water supply systems consisting of a domestic well and septic system are used throughout the world in areas where piped water supply and sewage are unavailable. In the United States, water quality in domestic wells is unregulated and septic tanks are generally only regulated by patchwork local requirements under the guidance of each state. The burden of clean drinking water falls to the domestic well owner, leading to the issue that water quality in households with private supply often fails to match water quality in public water systems. In residential areas, especially, water quality in private wells is threatened by septic leachate from other households. In this paper, we demonstrate that even households with contaminated wells have little incentive to maintain their septic systems when the source of contamination is unknown and they can simply install household water treatment. The socially optimal solution, however, requires regular septic maintenance from all residents. In other words, the economically optimal choice for each household conflicts with the socially optimal outcome. We model this social dilemma by coupling a groundwater transport model with a socio-economic model, incorporating incentives for septic maintenance and household water treatment. Our findings demonstrate that the socially optimal outcome can be achieved through individual optimization only when housing density is low. With high housing density, however, socially optimal outcomes can only be achieved through collective action. By incorporating human agency into the model, we demonstrate the failure of regulatory frameworks to create desirable outcomes (10-20% of septic systems in the U.S. are malfunctioning) and highlight policy recommendations that could improve resource allocation and governance of private water systems.