Incorporating on-site infiltration best management practices emphasizes using natural processes and green infrastructure to address stormwater quality and quantity problems. These approaches encourage on-site infiltration to reduce the number of pollutants that reach receiving water from stormwater. Infiltration is also used to replenish local groundwater supplies, but stormwater management in the arid West presents unique challenges. This presentation will explore why infiltration is not suitable or encouraged in the Las Vegas Valley – the driest large MS4 community in the nation. Following a discussion of the unique hydrologic and geologic features of the Las Vegas Valley that make infiltration unsuitable, the presentation will explore how the Las Vegas Valley municipal stormwater permittees have developed a regional approach to post-construction requirements, and how that approach benefits water quality. More specifically, the presentation will discuss stormwater quality features in regional detention basins, and requirements for BMPs in large parking lots and other new development projects.