Pipe mix-ups in houses pollute rivers and beaches

Dozens of homes in Auckland will have to have their water systems looked at after several properties were found to be wrongly pumping rainwater through the sewage systems - resulting in overflowing and pollution.

Manukau Water has begun inspecting and fixing residential water systems in parts of Spinnaker Bay and Howick, after a survey found that one in 20 homes in the region had their rainwater systems wrongly attached to the wastewater pipes.

Several problems have surfaced as a result, with sewage spilling onto private properties and water not being properly treated at the other end - leading to pollution of rivers, streams and beaches.

At properties where the rainwater was being channelled into the sewage system, it was important for people to understand the consequences of that and to rectify the problem quickly, Manukau Water chief executive Raveen Jaduram said.

"This is potentially a serious risk to public health and a lot of the problems are due to properties and watercourses.

"The excessive flows can also lead to reduced levels of treatment at wastewater treatment plants due to system overloading."

About 10,000 properties - most of them residential homes - were surveyed starting at the end of last year and throughout this year, after officials noticed unusually large amounts of water coming through the wastewater system during periods of heavy rain.

A smoke-testing technique - where a white, non-toxic smoke is put through the wastewater pipe - was used to pinpoint where various ventilation points or downpipes were faulty, by seeing where the smoke did or did not come out.

Another issue which resulted in overflowing was faulty gully traps.

People blocking them or smoothing them over was a big problem, especially during heavy periods of rain. Instead of going around the gully trap, it was going into the drain itself.

"Our aim is to inform customers of the possibility of rainwater infiltration into the system and to help prevent this by inspecting properties that might be at risk," Mr Jaduram said.

Properties in Mangere are next in line and other parts of the Manukau City region will be looked at in the next few months.