Since the temperature of shower drain water (SDW) is relatively high, lots of heat is wasted with the discharge of SDW. Therefore, the recovery of this unutilized heat from SDW shows great potential in improving the building energy efficiency. In this paper, a novel heat pump water heater assisted with SDW for small single family was proposed, which could effectively recover the energy in domestic SDW. To improve its performance, a shower waste heat extraction device (WHED) with water pre-heated loops was designed. A prototype of the system was firstly set up, and then the system performances under different conditions were experimented and discussed. The experimental results showed that approximately 70% of energy could be saved using this novel heat pump water heater, compared with the traditional electric water heater. Furthermore, the COP of the system could be improved observably when using water pre-heated loops. Thus the implementation of this novel heat pump water heater was verified to be capable of reducing energy usage and CO2 emissions significantly. (C) 2015 Elsevier Ltd. All rights reserved.