Groundwater in an urban and dense suburban setting is an often forgotten resource. Urban areas have frequently relied upon it for public drinking water supply, and in some urban settings, with water resources becoming scarce or more costly to use, it is once again under consideration as a potential water supply. Many urban areas have enthusiastically embarked on ambitious programs to infiltrate stormwater at the source without sufficient consideration of the impacts of highly concentrated recharge on groundwater levels and groundwater quality. Other “unintended consequences” of urban development include the impacts of subsurface construction on groundwater, and vice versa, with notable examples such as dewatering of ancient wood pilings and seepage into transportation-corridor tunnels at unexpected and potentially-damaging rates. In this session, both the role of urban groundwater as a source of supply and as a sink of excessive stormwater from highly impervious land uses will be examined.