The easiest way to “use” rainwater is its detention in places where it falls, and referral to the ground. Systems of rainwater utilization system can be implemented in different variants. In the simplest configuration it is a tank, with a runoff from the roof. The principle of operation of the tank (basin) is a method for rain water management. The article presents a practical application of methods of dimensioning infiltration basins by performing calculations showing how to alter the dimensions of the basin when changing the ground conditions while maintaining the same filling.