Water chlorination

The Council is temporarily treating Christchurch's drinking water with chlorine while it upgrades the below-ground 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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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.

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 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 53 pump stations across the city. From the pump station, the water flows directly out into our water reticulation system across the city. 

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 26 pump stations and 0.5 ppm at 27 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.  It will take until mid-June to implement the lower dose rate. Once that is done, the dose rate for each pump station will be indicated on the map below.

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 three pump stations where the well heads are secure and there is no chlorine at all. 

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 amount of work that needs to happen to remove chlorine is still being considered.

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.

There is detailed information in question and answer form here(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.