The aim of this study was to examine the temporal impact of rapid population growth between years 1987-2011 within the absolute, short-range, medium range and long-range protection zones of the two selected drinking water reservoirs of Istanbul, a typical megacity representing significant urbanization trend. Spatial distribution of land-use/cover and corresponding changes that have occurred in the various protection zones were analyzed via Landsat 5 TM images belonging to the inspected years. Drinking water reservoirs selected for this study were Omerli located on the Asian side, and Buyukcekmece situated on the European side of the city. The land-use/cover distribution were extracted from satellite sensor images based on the three classes; vegetation-V- (forests, green areas, parks, etc.), impervious layer-I- (settlements and transportation network) and soil-S- which constitute the main components of the Vegetation-Impervious layer-Soil (VIS) model. The areal analyses were conducted using VIS component analysis for the two different examined years. Striking information is obtained regarding the urbanization effects on the various protection zones. It is expected that the results obtained from the study will provide valuable information for the decision and policy makers of the megacity that are responsible for the sustainable management and development of the vulnerable and sensitive watersheds of the city that used to supply her water demand from the existing surface water bodies.