Abstract-With climate change now a reality rather than speculated possibility, the future change of rainfall pattern will affect the demand for potable water. Forth coming regulatory changes will mean that over 90% of UK homes will have their water usage metered, making consumers more and more aware of how expensive the commodity of "common or garden" water has become. In this paper the design of different rainwater harvesting systems (RWH) is evaluated for three residential properties of different roof areas. The design considered climate change effect and change in future rainfall for three periods 2020s, 2050s and 2080s under the high (AIFI) and low (B1) SRES scenarios in NW of England. The RWH systems were shown to fulfill between 25% and 85% of WC, washing machine and outdoor use demand making the system more valuable as a sustainable solution.