Pressure cleaning in Blacktown

At the 2021 Census, 81.1 per cent of occupied private dwellings in the Blacktown local government area were separate houses, against 65.6 per cent for New South Wales. Flats and apartments were 6.7 per cent. The council area held 121,337 occupied dwellings.

The suburb of Blacktown is a different mix. Separate houses were 65.4 per cent, almost exactly the state figure, and semi detached, row and townhouses were 18.6 per cent against 11.7 per cent for the state.

That townhouse share changes the shape of a job. A row of townhouses often shares a driveway or a common strip, so the question before a quote is who owns the concrete, one owner or the body corporate. Across the rest of the city it is the detached house job: walls, gutters, a driveway and a back patio.

Blacktown City Council says stormwater is rain that is not absorbed into the earth, and that unlike sewage it is not treated. The pipe network carries it straight into local wetlands and creeks, with any litter, garden waste, oil, heavy metals or other chemicals it has picked up.

Council's flood studies page says Eastern Creek drains approximately one half of the Blacktown local government area, a catchment of 118 square kilometres flowing to South Creek. Wianamatta South Creek is a tributary of the Hawkesbury Nepean River and drains a 640 square kilometre catchment in Western Sydney.

So a driveway in much of Blacktown sits upstream of Eastern Creek, and from there the Hawkesbury Nepean. Our answer does not change: the wash water is contained and recovered, not sent to the kerb.

Blacktown City Council runs a separate page on industrial stormwater pollution. It says industrial stormwater pollution presents a high risk to natural waterways, names oils and fuels running into drains as a cause, and runs a rebate for businesses that buy spill kits.

For a workshop, a warehouse yard or a loading dock in the area that is the brief in council's own words. Oil comes up with hot water and a degreaser, the bulk is picked up dry first, and the wash water is recovered rather than allowed anywhere near a pit.

The Bureau of Meteorology station at Prospect Reservoir records a mean annual rainfall of 877.0 millimetres, between Penrith Lakes at 756.3 and the coast. Relative humidity averages 74 per cent at 9am and 51 per cent at 3pm, and July nights average a minimum of 6.1 degrees.

Damp mornings and dry afternoons are the same pattern Penrith has. The south facing walls and the side paths hold the morning wet for longest, and that is where the green starts.