Many newer developments have 2 seperate sewer systems - a dirty water sewer for toilet flushes etc, and a storm sewer which collects water from street gutters. The storm sewers often are not treated, but discharge into streams,lakes or the ocean. This is rainwater and water from wastrels who overwater their lawns. It is still good!
I propose that along the storm sewer line there be deep areas which will function as cisterns. In wet seasons or in winter, the outflow tract will be left open and the water will rush along and out. In drier seasons the outflow tracts are closed and water will collect in the cisterns. This water could then be used to irrigate roadsides and public areas.
Sand and trash would also accumulate in the cistern, and this could either be removed or allowed to flush out in the wet season.-- bungston, Aug 07 2005random, halfbakery