Water management systems have been typically designed and operated under the assumption of stationarity. This assumption may no longer be valid under climate change scenarios. Water availability may change dramatically at some locations due mainly to possible impacts of changes in temperature and precipitation over streamflow volume and seasonality, adding pressure to water supply systems. It has been shown that snowmelt-dominated basins are particularly sensitive to such changes. Hence, human settlements and economic activities developed in such areas are particularly vulnerable. The Maipo river basin in Central Chile – where more than 6 million people live – is one of these areas. We used a calibrated water resources model of the Maipo river basin, in order to propose a general framework to evaluate adaptation options at the urban level. When comparing a mid-21st century period to a historic control period, results for three selected performance metrics showed a decrease in water system performance. Adaptation measures were evaluated in their capacity to maintain current water security standards. Two alternatives stand as highly effective options to this end: water rights purchases and improvements in water use efficiency. The political and economic costs of implementing these options, which could deem them unviable, are not considered here but are worthy of further research.