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.
Napier's water is drawn from the Heretaunga Plains aquifer, and has been filtered by natural processes through an artesian system shaped over millions of years.
Our water is then reticulated through some 481kms of pipe.
There are two main methods to clean the pipes, these being 'pigging' and flushing. We have increased our cleaning programme in response to the increased rate of dirty water issues that some customers have experienced since chlorination of the water supply.
In the week ahead of a scheduled cleaning run, we write to affected householders, advising of the disruption to the water supply and likely water discolouration.
Weekly radio adverts will be broadcast Friday to Monday providing information about which suburbs, streets and areas our water team will be operating in.
We will also update this website with the streets that will be affected the following day. The water supply isn't affected before 9am each day and cleaning is not carried out on Mondays and weekends. Find out the next day streets affected here.
The 2021 cleaning programme starts August and it is expected to run until October.
As a precaution we recommend to those households that have had their water mains cleaned, run your cold water tap at the end of the day to ensure your home plumbing is clear. Check out the FAQs for more information about what to expect.
This straightforward procedure involves minimal disruption to the water supply. A foam swab, called a "pig", is forced through the water main pipe, scouring it clean as water pressure propels it along to an exit point - another hydrant generally located several thousand metres further along the road.
Staff shut valves to control the direction taken by the pig. Travelling through the main at roughly the pace of a brisk walk, it emerges covered in biofilm. The pig is then discarded.
The majority of Napier and Bay View's pipes range from 75mm to 200mm in diameter. Pigs come in a variety of sizes. The diameter selected for cleaning a pipe is always larger than the pipe diameter - compressing the pig helps the cleaning action.
No cleaning agent is involved in the process. The pig is only 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 high 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. Pigging is undertaken during low water demand periods (late autumn, winter, early spring) to allow minimum interference to the supply.
Pipe flushing is usually undertaken when there are reports of dirty, discoloured water. It can also be undertaken as a planned mains cleaning activity where pigging is not an option due to various reasons (older cast iron pipes, diameter of the pipes, industrial areas, etc). Water is discharged through a fire hydrant or a scour valve at high flow, which picks up the sediments and biofilm in the pipe and removes them from the system. There is an all-year-round flushing programme in place throughout Napier and Bay View, focusing on problematic mains and cul-de-sacs (mains dead ends).
During every planned mains cleaning activity all discharged water is dechlorinated before entering storm water drains (using dechlorination mats and/or fire hydrant diffusers) to ensure minimum environmental impact.
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