Nappies and toilet bowls do not mix

Nappies are biodegradable in landfills, not sewers. In this case, it has just been dumped. Photo / APN

City works to educate residents after big rise in sewer blockages.

Residents in Hamilton's southeast are the city's biggest offenders for flushing disposable nappies, baby wipes and even McDonald's toys down the lavatory.

In the past two years the city's council has seen a rise in the number of blockages in the wastewater network and is trying to reduce it through improved technology and education.

Waters manager Tim Harty said it was difficult to pinpoint exactly what was causing each blockage because in most cases it was an accumulation of items.

"There's a whole raft of different things that tend to get flushed down, some intentionally and some not obviously. Lots of McDonald's toys tend to turn up in the system."

The 516 blockages in the network in the year ended June are likely to have been caused by several things, such as foreign items stuck in pipe joints, a displacement of the joints or tree roots growing through pipes.

The 62 blockages per 100km in the city's 798km wastewater network is slightly down on the year before's figures, but still higher than the council's target of fewer than 60 blockages per 100km of network.

In 2009/10 the figure was much lower at just 50 blockages per 100km.

Hamilton's southeast had a total of 208 blockages in 2011/12, almost double the northwest, which was the second-biggest culprit.

But Mr Harty said the exceptionally high number in the southeast, which covers older areas such as Claudelands, Hamilton East and Hillcrest

He said that could be due to a mix of factors.

These included the wrong things entering the system, more people living in the area because of the amount of high-density housing and the fact that its infrastructure was ageing.

He said the council was trying to educate people about what not to put down the toilet and that included disposable nappies, rags, fats and oils.

Mr Harty also said there might be a misconception that biodegradable nappies would degrade but this related to landfills, not sewers.

The council is also upgrading its own technology to help identify exactly where in the network the blockages are happening so appropriate upgrades can be carried out.