Water flow window is an energy efficient multi-glazing system with water flowing in the window cavity. Proper thermal insulation is crucial to enhance the related energy and cost saving. In this paper, the insulation performance of vacuum glazing (VG) and insulated glazing unit (IGU) in triple-glazing water flow window is explored. Experimental testing was completed during cooling season of Chengdu, China. The benefit of water application in window is also analyzed based on the testing results. The insulation performance of VG and IGU is found comparable when applied to water flow window in airconditioned space. The additional water stream is quite effective in lowering the glazing surface temperature. Comparing water flow window and those without water supply, the reduction can be as large as 4.81 ?C for inner glazing and reaches 10 ?C for outer glazing. Also, the inner glazing surface temperature fluctuation can be narrowed with water flow window, and the performance of VG insulation water flow window (VWFW) is more favorable comparing to IGU insulated water flow window (TWFW). Thermal performance of water flow window as thermal collector is also promising. The daily thermal efficiency of VWFW and TWFW are in the ranges of 24.69?45.95% and 21.9?36.13% respectively.