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Maintaining our networkTe tiaki i tō tātau kōtuinga wai

NCC’s mains cleaning programme flushes out the city's water pipes, removing (harmless) biofilm and preventing buildup. This is done with the ‘pig’, a foam swob forced through mains pipes, scouring them clean as water pressure propels the pig along to its exit point.

Water Mains Cleaning

Foam swab, called a pig, Water Mains Cleaning.Drawn from the Heretaunga Plains aquifer, Napier's water has been filtered by natural processes associated with an artesian system shaped over millions of years.

Our water is then reticulated through some 481kms of pipe.

The council's ongoing cleaning maintenance schedule, operated on a five-yearly cycle, flushes out the city's water mains, removing (harmless) biofilm that would otherwise continue to build up in the network. In the past, we've targeted 20 percent of the city's mains each year. However, the brown water issues some in the city have experienced since we since we began chlorination in May 2017 have meant we'll be doing more of the network in 2018.

The straightforward procedure involves minimal disruption to the water supply. A foam swab, called a "pig", is forced through the main, scouring it clean as water pressure propels it along to a predetermined exit point - another hydrant generally located several thousand metres further along the road.

Staff shut valves to feeder mains to control the direction taken by the pig. Travelling through the main at roughly the pace of a brisk walk, it emerges covered in sludge. The pig is then discarded.

Sixty to seventy percent of Napier and Bay View's pipes are asbestos cement, and diameter ranges from 75mm to 200mm. Pigs come in a variety of sizes. The diameter selected for cleaning a main is always larger than the pipe diameter - compressing the pig helps the cleaning action.

No cleaning agent is involved in the process. Then it is coated in a bactericidal grease to ease its entry to the hydrant. Before the water is discharged into the stormwater network, it is dechlorinated (using dechlorination mats) to ensure minimum environmental impact.

The CBD and Napier Hill are not included in the programme - the water pressure is not great enough for the cleaning method used, and cleaning the older cast iron, smaller diameter pipes could result in more problems than benefits. Generally the flow in these pipes is good, and dead-ends are flushed out regularly.

Public Notification

In the week ahead of a scheduled cleaning run, the council writes to affected householders, warning them of the disruption to supply and likely water discolouration.

Daily radio bulletins, broadcast between 7.00am and 8.30am Tuesday to Thursday on The Hits 89.5FM, Newstalk ZB 90.3FM and 1278AM and Coast 99.9FM, provide information about the movements of utilities division staff in the city.

The council also posts the streets that are going to be affected the day before on their website, these can be found in the public notices section. If there is any mains cleaning taking place at present then this is where you will find the streets been affected.

Supply isn't affected before 9.00am each day and no cleaning is carried out on Mondays.


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