Water is one of the most abundant energy sources in our environment and hydroelectric power has been one of the main forms of macro-energy supply. However, for harvesting green microenergy from water presented in our residential zone, industry or agricultural irrigation, traditional electromagnetic hydraulic turbine generator has limited applications due to its large size, complexity and high cost. Here we report a novel design of the multi-unit hydroelectric generator (HEG) for harvesting water-related energy based on contact electrification. The instantaneous output power density of the multi-unit HEG array is 0.07 W/m(2), which is 9 times of that from the individual HEG with the same dimension. Moreover, the rational design of the multi-unit HEG can increase the safety for its future service. By integrating with the multi-unit HEG, the household faucet can be a power source to supply clean energy continuously. Given the compelling features, such as, highly efficient, easily implemented, lightweight and extremely cost-effective, the multi-unit HEG renders a promising approach toward clean energy harvesting from ambient environment. (C) 2015 Elsevier Ltd. All rights reserved.