A circulating water system is widely used as a cooling system in process industries, and its energy consumption has a great impact on the energy performance of the whole plant. In a circulating water system, the pump network composed of main and auxiliary pumps offers power to the system, while the water turbine network recovers excess energy. A fluid machinery network in the circulating water system is then formed by the pump and water turbine networks. The difference value between the minimum theoretical power requirement of the pump network and the maximum theoretical power recovery by the water turbine network is the power target of the fluid machinery network. The power target is very significant for guiding the energy conservation of a cooling water system, as it means the theoretical limit of the network's energy consumption. In this paper, by analyzing influence factors on the power target in a fluid machinery network, the concept of effective heights of a branch and cooling tower is introduced to obtain the necessary condition of water turbine placement. Then a mathematical model to determine the power target in a fluid machinery network is proposed. A case study is used to validate the applicability of the model finally.