This paper examines some of the issues associated with the impacts of water demand management on the drainage network. In particular, it is argued that with the advent of lower water use WCs, much lower volumes and flow rates will be available to transport gross solids in sewers. The paper reports some of the results of a study to evaluate the performance of one such ultra-low flush WC in terms of limiting solids transport distance. It was found that the ultra-low flush toilet performed as well as a conventional WC, but only when connected to a 50mm diameter drainage pipe. The implication is that for best use of this technology, and other innovative devices, new building drainage design rules will need to be devised.

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