Fresh water is the most important source for maintaining of life and the main factor of sustainable development of all alive organisms. Growing population, expansion of production led to fast growing consumption of fresh water. The problem of deficiency of water resources becomes more extensive because of annual increase of water consumption. The aim of this article is to define the most optimum technology of fresh water replenishment. Having studied literature on this subject, we selected several methods of replenishment of reserves of fresh water: extraction of water from free air with using natural power factors, collecting rain water, bioengineering technologies with using of natural and technogenic systems; receiving fresh water by the stationary purifier "Rosa-1", ecological system for purification of a small-scale congestive water, and also the recirculative vertical bioreactor of a stream. Then compared them on three qualities: the cost of introduction of a method, efficiency and a serviceable life of equipment. By means of the analysis of results of comparison, we excreted the best technologies - collecting of rain water and bioengineering technologies with using of natural and technogenic systems, and the worst method - ecological system for purification of small-scale congestive water. We defined the best technology which will help to solve a problem of exhaustibility of water resources. Results of our research can be used for optimization of fresh water replenishment and further researches on this subject.