Up to 80% of energy for water supply to a 20-story building is used in the building. Buildings can reduce pumping energy by 45% by changing pumping systems. We extrapolated energy use for two high-rise pumping systems to city level. Replacing 25% of traditional pumping systems cuts annual emissions by 8600 tCO2e. Around 9% of China’s urban population uses 32% of energy for urban water supply.