Land use can alter biological, chemical and physical environmental processes. These alterations can be evaluated through water quality using a Water Quality Index (WQI). The WQI establishes water quality standards according to the altered environmental processes. Indiscriminate land use in Distrito Federal (DF) is the result of increased population and actual environmental impacts can be evaluated through studies of water quality. We used a Geographical Information System to analyze impacts on water quality at all public drinking water reservoirs over a period of 10 years (1994 to 2003) and related the observed water quality to types of soil and land use during the same period of time. The Distrito Federal covers 5814 km² and its soil types are mainly Oxic Rodhustox, Oxic Plinthustox and Typic Haplusept (Campos et al., 2000). Water quality at 30 public drinking water reservoirs managed by the Companhia de Água e Esgoto de Brasília (CAESB) in Distrito Federal was evaluated using the WQI, for a period of ten years (1994 to 2003). The WQI used by the CAESB is an empirical arithmetic equation, developed by the Scottish Development Department that uses the following parameters and their respective weights: fecal coliform (0.2), turbidity (0.15), color (0.1), ammonia (0.15), iron (0.15), pH (0.05) and DQO (0.1). Samples collected every month were averaged using WQI and grouped into two periods: wet and dry season, and then classified in five classes between excellent and very bad. These classes were assigned to their respective reservoirs and protected areas in an ArcGis 8.3 (ESRI) database creating 22 maps in a temporal sequence, i.e., two seasons per year for ten years. The resulting analysis showed that the majority of collection points have good water quality. Water quality is generally worse during the wet season due to rain. Samples collected in three districts: Mestre D'Armas, Barrocão and Pipiripau had medium or bad water quality. Land use at these three areas was analyzed using ArcGis 8.3. The Mestre D'Armas area has Typic Haplusept soil that is not appropriate for urban occupation and agriculture activity as it has been used. The Barrocão and Pipiripau areas have Oxic Rodhustox soil and are being intensively used for agriculture. Most public drinking water reservoirs are located near springs and our analysis has highlighted problems in water quality linked to land use near them. So, the situation probably is worse along the rivers.