Global climate change associated with rising atmospheric concentrations of greenhouse gases may alter regional temperature and precipitation patterns. Such changes could threaten the availability of water resources/Or rapidly growing Third World cities, many of which are already experiencing severe water supply deficiencies. This paper investigates the potential impacts of climate change on water resource availability for two Indian cities, Bombay and Madras. The paper begins by discussing future trends for population growth and water demand in each city. Nat, using climate change scenarios based on three general circulation models (GCMs), the paper assesses how climate change may affect water availability in the two urban regions. The assessment is conducted through the use of a monthly dryness index measuring potential evapotranspiration and precipitation. For each region, the dryness index under “normal” climatic conditions is compared with indexes created using GCM scenarios. The results of this assessment indicate that, unless large increases in regional precipitation accompany climate warming, higher rates of evapotranspiration will mean reduced water availability for both cities. The paper concludes by discussing some implications for water management in Third World cities.