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Information about chlorine and dirty waterNgā Pātai e Kaha Whiua Ana

Why is our water chlorinated? Pertinent answers to questions about why Napier’s drinking water supply is now chlorinated and what causes dirty water.

Information about chlorine and dirty water

The Havelock North Drinking Water Inquiry made a number of recommendations to improve safety of New Zealand’s water supplies and changes to our Drinking Water Standards.

The Government has identified that illness from the country’s public water supplies is significant, with up to 100,000 people getting sick every year. The uncomfortable reality is that New Zealand's water networks have probably been housing dangerous pathogens (bugs) for years.

Two of the main outcomes for Napier from the Havelock North Inquiry have been:

  • The raising of bore heads above ground level to stop surface water entering the bore and potentially contaminating the water.
  • Chlorination of the pipe network following seven minor contamination issues in our reservoirs and pipe system.

The water we extract from the Heretaunga Plains Aquifer is of a very high quality, however, like the majority of other public water supplies, our network is at risk of becoming contaminated. One of the ways to reduce this contamination risk is to have disinfection in the network, and this is provided by chlorine.

Any of the examples below could result in contaminants being introduced into our water supply network:

  • At the source or aquifer or through private bores.
  • Backflow (reverse flow) from houses or industry.
  • Damage to the pipes (eg. during excavation work or through vandalism, or asset failure).
  • Illegal access to water from fire hydrants.
  • Illegal connections to the water network.
  • Through pests and birds entering storage reservoirs.

Chlorine has been proven to be the most effective treatment for water supply networks for two main reasons:

  • It treats the water for pathogens (bugs).
  • It disinfects the pipes and reservoirs.

It is very likely that upcoming changes to the Drinking Water Standards will require a “disinfection residual” in New Zealand’s water supplies. It may soon be mandatory that our supply system is chlorinated.

It is our understanding that Christchurch City Council is finalising a major project to address risks related to their bores. As they make their bores safe they are removing chlorine.

We have already made our bores safe and have moved on to making sure our network is safe as well. We have added chlorine to help minimise the risks of contamination in our pipes and reservoirs after we had several positive tests for E. coli between January and November 2017.

Christchurch will also need to consider how they will maintain safety of their network and they will be working with their Drinking Water Assessor (DWA) to address this through their Water Safety Plans, just as we have with our Drinking Water Assessor (Hawke’s Bay District Health Board). Our DWA supports the decision to chlorinate Napier’s water as does the Ministry of Health.

Central Government is reviewing the regulations relating to Drinking Water. All indicators are that multi-barrier treatment processes and residual disinfection will be a mandatory requirement within the reticulation network.

The use of chlorine as both an effective treatment barrier and to provide residual disinfection is best practice worldwide and is cost-effective.

There are three main options that we could look at:

  1. Remove chlorine and accept the risk
  2. Continue to manage risk with chlorination
  3. Change our network to remove chlorine and minimise risks (Netherlands model)

Both the Hawke’s Bay District Health Board (our Drinking Water Assessor) and Napier City Council are not willing to risk lives by removing chlorine from the water. Chlorine is the most cost-effective, efficient way to minimise contamination risks in our network.

To bring the Netherlands model to Napier we would need to reduce network leakage from our current 22% (typical for a water network like ours) to less than 5%. We would need to replace large parts of our network (potentially 55% at $72m), and add extensive monitoring and control infrastructure (several more million dollars), changing the way the network operates.

The Netherlands model works due to high population density and took over a decade to change. The costs of operation are likely to be 5-10 times what we currently charge our ratepayers for water. Napier residents currently pay around $240 per household annually for unlimited water supply. Changing the network would likely increase the ongoing costs per household to over $1,200 per year. There would also be a large cost initially to rebuild the network and rough costs indicate that this could increase rates by around 20% annually for a ten-year period. This is likely to be uneconomic for our community.

There would still be chlorination in the network during contamination events and there would be boil water notices during these events.

We have many drinking water projects planned and underway. You can read more details about them here.

  • Three bores have been brought above ground
  • Upgrades have been made to underground bore chambers to make them safe
  • Close down of two bores that didn't meet requirements
  • Improvements to water reservoirs
  • Introduction of chlorine treatment at the source
  • Increased planned maintenance of the supply system including extensive mains cleaning projects to remove biofilm (the accumulation of organic and inorganic matter attached to the insides of pipes and water storage tanks) from our water network.

We have put more money into water supply.

In the first three years of the current Long Term Plan, we are spending about $250,000 per year. From year 2021/22, we will be increasing our spending on pipe replacements and over next 30 years we have planned to spend over $30m for pipe replacement. These costs exclude the larger capital spend that is planned for new water related projects.

Major projects take resources and planning and take time to implement. We have brought a number of significant projects forward and our ability to deliver this accelerated programme will have its challenges.

We are going to accelerate our pipe cleaning programme. This progamme will be implemented during the winter periods when the water demand is low. We are also planning to change the way our water supply is operating by introducing new water bores and making changes to the pipe network. These are major projects and will help to reduce the water clarity issues. These projects might take at least three years to complete. With these works, we will experience gradual improvements of our water clarity issue.


More than $150 million, and it wouldn’t necessarily make it safer – there could still be breaches to the pipework from accidental and intentional breakages, and illegal connections. A complete replacement would need to be done in stages to minimise disruption. This would take more than a decade and would add significant increases to rates without the desired benefits and reduction in health risks.

Our water source, the Heretaunga Aquifer, has naturally occurring manganese - one of the most abundant metals in the earth's crust. When manganese-laden water mixes with oxygen or chlorine, the manganese oxidises or changes state to manganese dioxide, a black solid that can coat the inside of pipes.

Manganese has always been present in our water network. Dirty water is now more of an issue due to the manganese reacting with the chlorine we've been adding to our water since 2017. 

In Napier, this affects certain suburbs (Tamatea, Onekawa and Pirimai) more than others because of different water pressure and flow rates, and because there are higher levels of manganese in the aquifer bores that supply these suburbs.


Open your outside tap until the water colour clears. If it doesn’t clear after 15 minutes, phone our Customer Service Centre on (06) 835 7579. To help with water conservation, don't let the taps run for more than 15 minutes. Please call us if the water hasn't run clear after this time.

If you do resolve the problem yourself, we'd really appreciate a heads up that you've had problems. Please complete the 'Report It' form.

If you are unhappy with the taste of the chlorinated water, you can leave the water in a jug for a few hours and the chlorine will dissipate. Bench top jug filters are also useful.

If you experience a very strong chlorine smell, similar to a swimming pool, this generally indicates that the chlorine is doing its job, not that there is a really high level of chlorine in the water. We need to know if you have a really strong chlorine smell so that we can check it out.

You can call us on our Customer Service Centre on (06) 835 7579 or complete the 'Report It' form.

Napier's source water has a manganese level of less than 0.07 mg/L, well below the manganese Maximum Acceptable Value of 0.40 mg/L. This is safe to drink.

The dirty tap water some households have been experiencing has higher levels of manganese and should not be drunk. 

If you've experienced dirty water issues in the past, we'd recommend you run your laundry tub taps first before you do your washing. If your water isn't running clear, then run your outside tap hard for up to 15 minutes. If things still look murky, then call our 24/7 Customer Service number - 0800 4 NAPIER - and we'll send our team out ASAP. To help with water conservation, don't let the taps run for more than 15 minutes. Please call us if the water hasn't run clear after this time.


The first dechlorinated water station, located on the south east corner of Anderson Park (York Ave side) opened in mid-2019. The water station has four taps and users aren't charged anything.

A second dechlorinated water station located close to the city centre is scheduled to be ready in 2020/21.


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