The paper deals with the effective management of rainwater. Given the current climate change, which is currently faster than anticipated, environmental issues are very timely. These sudden changes are mainly caused by human activity. The most noticeable climate change is the increase in temperature and changes in the rainfall regime. These two changes are closely linked. The average consumption of drinking water per capita is over 100 liters of water per day in civilized advanced nations. But about 50% of this consumption does not need to have quality drinking water, so rainwater can be used as a substitute. The basis of success is its correct collection and subsequent storage. The aim of the paper is an optimization of the design of a suitable system of use of rainwater in households and its evaluation from the financial point of view. The purpose of rainwater systems is to minimize water consumption from the water supply system and to effectively use rainwater in the household while achieving cost-optimal levels. There is also an effort to reduce the amount of rainwater drained away from the land to lessen the sewerage network and reduce the risk of flooding.