Small reservoirs play an important role in supporting the local economy in the savannah areas of Brazil and are primarily used for the provision of water for irrigation and watering livestock. Hundreds of small reservoirs have been built in the last few decades in the Preto River Basin, but efficient water management and sound planning are hindered by inadequate knowledge of the number, storage capacity and spatial distribution of reservoirs in the basin. The main reason for the lack of this information is that current methodologies for quantifying the physical parameters of reservoirs are laborious, time consuming and costly. To address this lack of data, a simple method to estimate reservoir storage volumes based on remotely sensed reservoir surface area measured with LANDSAT was developed. The method was validated with a subset of reservoirs in the Preto River Basin for which surface areas, shapes and depths were determined with ground-based survey measurements. The agreement between measured and the remotely sensed reservoir volumes was satisfactory, indicating that remotely-sensed images can be used for improved management of water in the Brazilian Savannah region. With the newly developed methods we found that the Preto River Basin’s 147 small reservoirs can store 19 × 106 m3 of water at full capacity.