Urban environments significantly alter physical and chemical hydrogeologic settings. The physical alteration of the landscape can change recharge, groundwater flow dynamics, and local water balances. Microbial contamination of water sources due to wastewater is an ever-present threat, but contamination by metals and industrial compounds is a long-term concern in cities with industrial economies. The hydrogeologic setting and the age and wealth of a city are important factors influencing the magnitude of the impact on and the recovery of a hydrogeologic system from urban activities. Urban environments can have unique influences on water geochemistry, making delineation of site-specific urban geochemical markers necessary to quantify the extent of urban effects on water quality.