Re-engineering the urban drainage system for resource recovery and protection of drinking water supplies.

The Harare metropolis in Zimbabwe, extending upstream from Manyame Dam in the Upper Manyame River Basin, consists of the City of Harare and its satellite towns: Chitungwiza, Norton, Epworth and Ruwa. The existing urban drainage system is typically a single-use-mixing system: water is used and discharged to "waste", excreta are flushed to sewers and eventually, after "treatment", the effluent is discharged to a drinking water supply source. Polluted urban storm water is evacuated as fast as possible. This system not only ignores the substantial value in "waste" materials, but it also exports problems to downstream communities and to vulnerable fresh-water sources. The question is how can the harare metropolis urban drainage system, which is complex and has evolved over time, be rearranged to achieve sustainability (i.e. water conservation, pollution prevention at source, protection of the vulnerable drinking water sources and recovery of valuable materials)? This paper reviews current concepts regarding the future development of the urban drainage system in line with the new vision of "Sustainable Cities of the Future". The Harare Metropolis in Zimbabwe is taken as a case, and philosophical options for re-engineering the drainage system are discussed.