The purpose of this article is to choose the most cost-effective water supply system for the high-rise building in St. Petersburg. For this task the high-rise building was modelled. Two types of water supply systems were considered for this building: without zoning and with parallel zoning. The hydraulic calculation was made for the same work conditions. The calculation shows that total losses at the network system with parallel zoning are less than in the system without a zoning. As a result, author came to a conclusion that system with parallel zoning is the most cost-effective for the high-rise building.