Impermeable surfaces (e.g. cemented surfaces and canals) associated with the urban fabric alter natural watercourses and water flow regimes. Hard, impenetrable surfaces contribute to the risk of flash floods, which can result in the damage and/or destruction of both grey (build-up) and green infrastructure. This highlights the role of vegetation and permeable surfaces in reducing flood risk through slowing down flood water and increasing infiltration. This regulation of water regimes concurrently provides other services such as water purification.