Water chlorination

The Council is temporarily treating Christchurch's drinking water with chlorine while it upgrades well heads. Temporary chlorination provides an extra level of protection against waterborne illnesses.

Tap water in Christchurch city is still safe to drink. The quality of the groundwater remains excellent, and we test it daily to ensure it is free of bacterial contaminants. 

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Hot water cylinders

A hot water cylinder.

The temporary chlorination of Christchurch’s water supply is being linked with an increase in hot water cylinder failures. We've answered some of the commonly asked questions about the issue.

Why are hot water cylinders failing?

Christchurch has historically had issues with hot water cylinder failure. Certain areas of the city, such as Cashmere, have been affected more than others.

We are still working with the industry to better understand the scale and possible causes for the increased rate of failure over recent months.

There are multiple factors that can lead to a hot water cylinder leaking, and then needing to be replaced. These include: the chemical composition of the water, the age of the cylinder, the type of cylinder, whether there is any debris in the cylinder, and the particulars of the installation.

We have been working with manufacturers and it appears the majority of the cylinders that are failing are reported as older, low pressure copper cylinders.

What is your response to the University of Canterbury report?

We have had the chance to consider the University of Canterbury report and the conclusions reached. We agree that the presence of chlorine in the water, along with the other factors noted in the report (such as temperature, details of installation and water chemistry), has contributed to the observed pitting corrosion. We similarly agree that pitting corrosion of hot water cylinders is likely to become more frequently observed.  Whether or not this extends to other copper plumbing fittings is yet to be determined.

Why are other parts of New Zealand not having large numbers of hot water cylinder failures?

The chemical composition of water supplies around the country is quite different.

Places like Auckland and Wellington use surface water (from rivers and streams) which generally develops a protective film when in contact with copper plumbing.

In Christchurch, we are using groundwater (from aquifers).

Pitting corrosion leading to pinhole failure happens more commonly in some bore water (underground) supplies.

In Hastings and Napier, for instance, they have bore water supplies and also experienced a rise in hot water cylinder failures following chlorination of their water networks. Napier and Hastings found the number of failing cylinders decreased over the year after chlorination was introduced.

What does the Council say to people who have had to repair or replace their cylinder? 

We understand that having to replace your hot water cylinder is a costly exercise and we also acknowledge that there has been an increase of hot water cylinders failing since the introduction of chlorine.

It’s important to remember there are multiple factors as to why pitting occurs in hot water cylinders. These include: chemical makeup of the water, age of the cylinder, type of cylinder used, debris in the cylinder, and the quality and thickness of copper used. Because of this, the Council is not compensating property owners.

We are continuing to monitor the situation and work with manufacturers and suppliers to gain further understanding. Work is also progressing on our well head remediation programme to reduce the chlorine levels in our water.

What cylinders should I buy if I need to replace mine?

There are specific cylinders that are sold for areas where pitting corrosion is prevalent. If you are replacing your cylinder talk to your plumber about the best option for your area. Some options include enamel-lined steel or stainless steel cylinders.

Could chlorine also impact my gas systems or pipes?

There is no evidence of an increased number of failures in copper heat exchangers in gas continuous flow units, copper water pipes, or other fittings.

Latest updates

Latest newsletter: Water Supply Update 31 October(external link)

Rolling updates: The word on water: Latest on chlorination(external link)(external link)

News archive

New dial tracks city water use(external link) (13 November 2018)

UV disinfection in pipeline at city's biggest pump station(external link) (17 August 2018)

Council finalises upgrade plan for 72 wells(external link)  (7 August 2018)

Chlorination stops at two more pump stations(external link) (31 July 2018)

Pump stations targeted for end of chlorination(external link) (14 June 2018)

New 12-month role to focus on drinking water(external link) (7 June 2018)

Council moves to lower chlorine level(external link) (28 May 2018)

Pipes flushed to reduce chlorine taste(external link) (24 May 2018)

Why does the taste and smell of our water vary?(external link) (17 May 2018)

Council agrees approach to well head work(external link) (26 April 2018)

Chlorine roll-out almost complete(external link) (20 April 2018)

Water supply well heads may be moved above ground(external link) (10 April 2018)

Riccarton and north-west zones next for water treatment(external link) (3 April 2018)

Final preparations under way for temporary chlorination(external link) (23 March 2018)

Date set for temporary chlorination of city's water(external link) (12 March 2018)

Council agrees scope of water review(external link) (8 February 2018)

Council agrees to temporarily chlorinate  water(external link) (25 January 2018)

Council releases water report(external link) (24 January 2018)

Well inspections reveal contamination risk(external link) (23 January 2018)

Water review findings – 16 October 2018

On 16 October we released findings of the independent review: Management of Bore Water Security undertaken by consultant Bruce Robertson.

In his review Mr Robertson acknowledges the Havelock North drinking water contamination incident in 2016, which resulted in a widespread gastroenteritis outbreak, resulted in more rigorous assessment processes being applied by external assessors to the drinking water standards.

The review identifies a number of issues within the Council’s Three Waters Unit, including:

  • A lack of a cohesive system to manage compliance with all three criteria required for bore water security. The Three Waters Unit over-relied on one of the criteria requiring E.coli to be absent from the water. It needed to provide more reporting on the other two which are security of the water source and whether it was possible for contaminants to enter the water supply through the well heads.
  • A general failure to escalate the developing issue with the below-ground well heads.

The review says it is unlikely we could have prevented the loss of secure bore status, and the subsequent temporary chlorination of our water, even if we had got this right in the second half of 2017.

Steps have been taken to address the issues raised in the report. Our key objective is to be able to return unchlorinated water to our community which is why we have put in place a comprehensive water supply improvement programme ahead of the report being received.

The report was commissioned by Chief Executive Dr Karleen Edwards.

Read the report and our Newsline article(external link) for further information.

Chlorination, the water network and Havelock North impact

What you need to know about our network and how we're working to maintain a safe drinking water supply.

What the Drinking Water Standards say

In order for groundwater to be provided without the need for treatment, three criteria must be met:

  1. The bore water must not be directly affected by surface or climatic influences (i.e. the water is at least a year old, by which time any pathogens will have died)
  2. The well head must provide satisfactory protection to prevent contamination of the water supply
  3. E. coli must be absent in the bore water.
A water supply well head.

Well heads are regularly inspected.

To meet the first criteria, every five years we test the age of the water in a selection of wells and undertake groundwater modelling of our aquifers.

To meet the second criteria, we have an independent expert in well head security regularly assess all well heads, with each well head inspected once every five years.

Our regular testing for bacteria and lack of transgressions provides the evidence to satisfy the third criteria.

This information is provided to the Drinking Water Assessor to demonstrate that our groundwater supply is secure.


About our water infrastructure

The Council has 104 wells with below ground well heads and 36 wells with above ground well heads. There are 53 pump stations that supply water across the network. 

A well head is the physical structure at the top of the well that connects to the water supply network.

All new well heads are built above ground to improve the resilience and safety of wells and the security of water supply, and this has been Council’s approach for all new wells drilled since the earthquakes.


The impact of the Havelock North drinking water contamination event

After the earthquakes, the Council was granted provisionally secure status for its water supply. Well head security assessments were done with 20 per cent of the well heads being assessed each year, meaning the entire network was completed over five years.

In May 2017, the Havelock North Drinking Water Inquiry Stage 1 report was released. It identified below ground well heads as a possible source of water contamination. The Council asked its maintenance contractor Citycare to investigate the condition of its below ground well heads.

A below ground well head.

Some below ground well heads were identified as needing remediation work.

In August that year an improvement programme began to address the potential pathways for contamination via well heads – sealing cracks, raising air vents etc.

In December 2017 the Stage 2 Havelock North Drinking Water Inquiry report was released. That month the Council’s well head security expert did assessments of 25 well heads. They applied a stricter interpretation of the standards and found that the well heads were no longer regarded as being secure from contamination. Later that month, the Drinking Water Assessor advised Council that the groundwater supply was no longer provisionally secure.

In January, on the advice of staff and the Medical Officer of Health, the Council decided to temporarily chlorinate the water supply for up to 12 months while well head remediation was done.


What the government is doing

The Government is undertaking a nationwide review of Three Waters and considering its response to the recommendations of the Havelock North Drinking Water Inquiry. These include the formation of a single regulatory body and reviewing the Drinking Water Standards. Among the recommendations of the Havelock North Drinking Water Inquiry are:

  1. The mandatory treatment of drinking water supplies in New Zealand to protect all water supplies from bacterial and protozoal contamination
  2. Removing the “secure bore water” status from the Drinking Water Standards of New Zealand
  3. Prohibiting new below ground well heads
  4. The creation of a single water regulator in New Zealand.
  5. That the Drinking Water Standards for New Zealand be reviewed.

What we are doing

We are upgrading our well heads so they meet the new, stricter interpretation of the Drinking Water Standards. Once well heads are secure, temporary chlorination can stop at those sites.

We are also looking at whether UV light is an appropriate treatment method at some sites. UV treatment provides protection against contamination but does not have the same effect on taste and smell as chlorination.

Some well heads will be converted to above ground well heads to further improve their security and to make them easier and safer to access for maintenance. There will be some new wells drilled. Other work will be done to provide protection from contamination in line with the stricter interpretation of the standards.

The immediate work we're doing is shown on the map below under Stage 1 works. There is more detail about this work on the well head improvements webpage.

Our work is being planned so that whatever option we do to remediate our well heads or provide an alternative to chlorination, it will meet the best practice for water supply infrastructure.

Reducing the amount of chlorine in the system

Reducing the dose rate

Our agreement with the Drinking Water Assessor is to dose at a rate of 1 part per million (ppm) after 60 seconds' contact time at some pump stations and 0.5 ppm at other pump stations where there is two minutes' contact time.

Contact time is how long chlorine spends in the water before it is distributed for consumption. This means we must maintain 1 part per million at a distance along the pipes that water travels in a minute, or 0.5 ppm at the distance water travels in two minutes.  

The map below will be updated to show the target dose rate for each site.

Favouring secure above ground well heads

Some pump stations are supplied by a mix of below ground and above ground well heads.  Minor remedial works are being carried out to 23 above ground well heads at seven pump stations to enable these well heads to be signed off as secure.

The works include installing and/or raising air valves (above the 100-year flood level), sealing around cables, sealing any cracks and/or installing new concrete plinths around the well head. This work is expected to be completed by the end of July.

We will also isolate the below ground well head so no water is being taken from it. This procedure has been accepted by the Drinking Water Assessor and means water from these pump stations will not be chlorinated.

The pump stations include:

  • Burnside, Grampian, Thompsons and Farrington in the North West zone
  • Hills and Lake Terrace in the Central zone
  • Woolston in Ferrymead.

Taking the bores with below ground well heads out of service is only possible at times of low (winter) water demand.

Taste and smell

What causes the chlorine taste and tips on how to reduce the effect

Initially when water supplies are chlorinated you will notice a stronger smell and taste although this should reduce over time. 

Council contractors are flushing pipes in areas most affected by the smell and taste of chlorine.

The pipe flushing is one of a range of options to help reduce the smell and taste issues people are experiencing. Staff are also working with the appropriate health authorities to explore how we can reduce the amount of chlorine being added into the water supply.

When we dosed after the earthquakes, we did notice higher levels of taste and smell at the beginning of the chlorination. That was due to the oxidation of the biofilms and organic matter through the system. The taste and smell did improve over time and we expect that to happen this time too.

There are 53 pump stations across the city. While you will be primarily supplied by one pump station, if you are midway between pump stations, sometimes you may be getting the water from one pump station and sometimes the other. The level of chlorine in those pump stations may be different. If you live close to the pump station, the chlorine dose you get coming out of your kitchen tap will be higher than if you live much further away.

If you are concerned about the taste, you can keep drinking water in an open jug in the fridge. The chlorine taste will dissipate naturally over a few hours.

Chlorine and any associated by-products can removed by using a granulated, activated carbon (GAC) filter. These are available from hardware supplies stores and water filter companies.

Health and wellbeing

What to do if you have a skin condition or sensitive skin

There are no known health impacts from drinking water effectively treated with chlorine and it is safe for pregnant women to drink. 

The quality of the groundwater remains excellent and it is tested daily to ensure it is free of bacterial contaminants.

The amount of chlorine dosed into the water supply will be carefully managed to ensure levels of chlorine in the water people drink are minimised. 

The use of filters will mitigate any risks for those on dialysis. This is being arranged by the Canterbury District Health Board.

Chlorine can be an irritant for an existing condition such as asthma or eczema. If you feel your skin getting dry or itchy, use moisturiser after having a shower or bath. If you notice increased skin irritation, asthma symptoms or other symptoms – seek medical advice from your GP. 

In Canterbury you can call you usual GP’s number after-hours and your call will be put through to a nurse who can provide free health advice.  You can also contact Healthline any time on 0800 611 116 for free health advice. 

Looking after pets and fish

Treated water is safe for household pets such as cats and dogs to drink.

If you have fish in outside ponds you will need to either turn down in-coming water to an absolute trickle (this dilutes the chlorine level to a safe amount for your fish), or fill up drums of water and let them sit for at least 24 hours before using (the UV of the sun evaporates chlorine).

For fish tanks or bowls inside, fill up a container of water and let it sit for at least 24 hours and then only replace one third of this water at a time with what is in the tank already. If you’re still worried, you can buy de-chlorinating kits (sodium thiosulfate) at pet supplies stores.

About temporary chlorination

Why we're treating water and how it's done

Water chlorination is the process of adding chlorine to the water supply to keep it safe from harmful bacteria. Sodium hypochlorite is used in Christchurch. It can be added as a precaution after routine work, such as reservoir cleaning, or as a result of finding bacteria in the water supply during routine water sampling.

Water treatment in Christchurch.

Drinking water in Christchurch is being temporarily treated with chlorine.

The Christchurch water supply is made up of several zones that operate independently of each other. While the main city urban supply is being temporarily chlorinated, supplies for Akaroa, Duvauchelle, Little River and Takamatua are permanently chlorinated. We will also be temporarily chlorinating the supply to Wainui.

We have to chlorinate the water supply because the below ground well heads on the groundwater wells servicing our city are no longer deemed secure. Monitoring shows there is a very small risk of contamination entering the water supply through the well heads. Public health professionals advised us we needed to chlorinate provides that an extra layer of protection, just in case.

The chlorine dosing takes place at pump stations across the city. From the pump station, the water flows directly out into our water reticulation system across the city. 

We are testing the chlorine levels daily from different points in the system and adjusting our dose where needed. All results are well below the maximum set in the New Zealand Drinking Water Standards (5 parts per million). 

There are four pump stations where the well heads are secure and there is no chlorine at all - Estuary, Keyes, Prestons and Gardiners. 

Chlorine is a powerful oxidising agent. As it travels through the system, it will react with any organic matter, such as slime build-up in the pipes. It might also react with iron in the old cast iron mains and it will react with any other organic material it comes across.

The Council (governance) has authorised the chlorination of the water supply for up to 12 months. Should longer be required, a further resolution of Council would be needed.

The Council also resolved that, long term, it wants to retain the city's untreated water supply system and will oppose any Government moves to impose mandatory permanent chlorination.

 

Detailed information in question and answer form(external link)

Timeline of events

Temporary chlorination milestones

Post-earthquakes

Post-earthquakes

Below ground well heads declared provisionally secure with regular assessments done.

May 2017

May 2017

The Havelock North inquiry stage 1 report is released and identifies below ground well heads as a possible source of water contamination. The Council gets its contractor to investigate the condition of its below ground well heads.

August 2017

August 2017

In response to the investigation of below ground well heads, the Council begins an improvement programme.

December 2017

December 2017

New security assessments are done and find that the well heads assessed do not meet the standard to be declared secure. The Drinking Water Assessor advises that the water supply is no longer provisionally secure.

25 January 2018

25 January 2018

Following discussions with the Canterbury Medical Officer of Health, the Council decides to temporarily treat the city’s water supply while the well head upgrade work is done. It is expected to take about two months to set up temporary chlorination.

26 March 2018

26 March 2018

The Council begins temporary chlorination of the city’s water supply.

Where have we chlorinated

Map Listing

For more information

You can email specific questions to watersupply@ccc.govt.nz or call (03) 941 8999 or 0800 800 169.