A sponge city is a new urban construction model for flood management, strengthening ecological infrastructure and drainage systems, proposed by Chinese researchers in early 2000. The Sponge City philosophy is to distribute and retain water at its source, slow down water as it flows away from its source, clean water naturally and be adaptive to water at the sink when water accumulates – this is in stark contrast to the conventional solution of grey infrastructure, which is to centralize and accumulate water using big reservoirs, speed up the flow by pipes and channelized drains, and fight against water at the end by higher and stronger flood walls and dams.