Stormwater runoff became more problematic as the cities grew and more of their area was covered with impervious surfaces. The volumes of water were so great that it was infeasible to manage the runoff by using the sewerage system, so separate stormwater drainage systems were developed. They, too, drained directly into rivers, harbours, bays and oceans that abutted the cities and became significant sources of pollution of those waters.

The early decision to develop separate systems for sewerage and stormwater drainage meant that wastewater flows could avoid the peaking problems associated with storms — problems that would only be exacerbated as development of the cities led to the increasing coverage of drainage catchments by impervious surfaces. Although sufficient water falls as rain in the urban areas to meet their water requirements, this approach to stormwater management means that, even today, stormwater is discarded and treated as a ‘problem’. How much of this is a consequence of the fact that surface drainage, as distinct from sewerage, was the responsibility of local government whereas in many cities sewerage was the responsibility of the water-supply authority has been little explored. It is interesting to note that in the recent drought some thought has been given to the possibility of redirecting stormwater, on occasion, to ensure that the sewers were properly flushed — the combined effect of water restrictions and water-saving behaviour having reduced sewage flows so that the systems had a tendency to block.