This paper deals with a part of the preliminary results of three years investigation activity, carried in Dar es Salaam coastal plain (Tanzania), ACC-DAR project, supported by the European Union, in cooperation with Sapienza University of Rome and Ardhi University of Dar es Salaam. Here, they are presented the effects of rainfall data evolution in the last 50 years on the groundwater active recharge, due to land cover evolution. As a matter of fact, in the last fifteen years the Dar es Salaam coastal plan has been involved in a hard increasing of groundwater exploitation, due to increased population. On the on the hand, the groundwater active recharge has been decreased, due to the evolution of land cover. In the framework of the project, the rainfall data have been collected referred to 50 years of observations in the three urban stations of Dar es Salaam. Starting from the data collection of the continuous historical rainfall series, it has been evaluated the groundwater active recharge for different land cover scenarios from remote sensing data. The results have been compared to water demand evolution values, referred to the same temporal range, and it has been outlined that in the last few years the water demand, in this area, has overpassed the groundwater active recharge.