Over the past twenty-five years, per capita water use has declined in many US cities. Technological and policy changes partially explain this decline, but variables beyond the control of water managers also influence water use including external (e.g. drought) and emergent (e.g. public attention) changes. Importantly, these variables interact and the relationships between these variables and water use are non-stationary. However, many models assume fixed relationships between water use and its drivers, and limited interaction between variables. Here we present a flexible socio-hydrological approach to model how conservation strategies, and external and emergent changes, interact to influence per capita water use. We apply this approach to Las Vegas and find that marginal water rates, code changes coupled with population growth, and conservation response to water stress are the key drivers of the observed decline. Critically, modeling these strategies in absence of their connections to population growth and water stress cannot fully account for observed changes.