This publication reports on the hydrological impacts of urbanization, which are broadly categorized as follows: changes in water budget, perturbations of hydraulic conditions, and pollution and degradation of water sources. The following studies are described: geochemical and isotopic tracers of recharge and reclamation of stormwater in an urban aquifer, Adelaide, South Australia; and the combined use of chemical and isotopic information to model the effects of stormwater infiltration on groundwater quality in an urban fractured rock aquifer, Auckland, New Zealand.