Water Chlorination

Chlorine is used as a preventative measure against contamination because it kills the bacteria that can get into water supplies and spread disease, helping ensure supplies are safe to drink.

New Zealand’s drinking water rules are changing. The new Water Services Act 2021 came into effect on 15 November 2021 requiring all Councils in New Zealand to be able to provide residual disinfection (chlorine) for all public drinking water supplies and for all supplies to be chlorinated by 15 November 2022, unless they have an exemption from the drinking water authority Taumata Arowai.

This is to keep drinking water safe.

All water on Selwyn supplies is treated at water treatment plants before it enters the pipes to your property. Chlorination provides an additional safe, effective treatment through the pipes, all the way up to your tap.

Chlorination has been used safely and effectively all over the world for around 120 years as a preventative treatment to avoid contamination of water supplies. It keeps millions of people all round the world safe from waterborne disease, including the majoirty of New Zealanders.

Chlorine has been used safely all over the world for around 120 years. It keeps millions of people all round the world safe from waterborne disease.

The majority of New Zealand’s drinking water is chlorinated. In Selwyn we have nine water supply schemes that are already permanently chlorinated, providing effective treatment to keep the water safe for those communities.

The amount of chlorine added to the water supply is carefully managed to ensure levels of chlorine in the water people drink are absolutely minimised.

Chlorine levels are monitored continuously at our treatment plants to ensure the levels are safe. Monitoring equipment is also being added throughout the networks over time.

Chlorine and cancer

The International Agency for Cancer Research (IARC) does not believe chlorinated water is either a probable, or even possible, cause of cancer.

Chlorine has been used safely all over the world for around 120 years. It keeps millions of people all round the world, including most of New Zealand, safe from waterborne illness.

The Journal of the National Cancer Institute acknowledges that “water chlorination is one of the major disease prevention achievements of the 20th century”, and that it “has become the principal means of effectively reducing waterborne enteric diseases”, which the World Health Organisation has stated account for a significant number of deaths every year, even in developed countries.

The Council has begun the process of applying for exemptions for our water supplies – to our knowledge we were the first Council in the country to apply for an exemption under the new rules.

We’re applying on a scheme-by-scheme basis for our unchlorinated supplies, using a risk-based assessment, starting with the lowest risk schemes first. As this is a new process we don’t know how long it will take to get a decision from Taumata Arowai.

If we are unable to gain an exemption for a supply then chlorination will become permanent as required by law.

We are also assessing the cost to upgrade those supplies that do not qualify for an exemption. Upgrades will need to covered by rates and the Council has committed to discussing this with our residents once we have a clearer idea of the costs to gain exemptions for our supplies.

In the early stages of chlorination you might notice a slight change in taste as the new treated water moves through the scheme and mixes with unchlorinated water in the Council’s reservoirs. However, most users report that this settles after the first few days.

At the minimum dose most people should not be able to smell or taste chlorine. However, the smell and taste of chlorine increases when the chlorine is consuming any organics, or when the dose is increased. So being able to smell or taste the chlorine could mean that it is doing its job of treating anything that could make your drinking water unsafe. Alternatively it could mean that the dose has been increased due to a specific situation where we’ve needed to add more to keep the water safe.

The new rules require that we have a minimum dosage of 0.2 parts per million (ppm) in the water when it reaches each property on the supply.

The amount of chlorine dosed into the water supply is carefully managed to ensure levels of chlorine in the water people drink are absolutely minimised. This dosage may vary at specific times if it is needed to keep your drinking water safe.

Public consultation on the Water Services Act 2021 was run by the Parliamentary Health Select Committee in March 2021 as part of the Parliamentary process for the passage of the bill. You can find the Council's submission on the bill here [PDF, 202 KB].

You can install an under-bench filter or fill a jug of water and leave it on the bench or in your fridge overnight. The chlorine will dissipate naturally over a few hours.

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

What to do if you don’t want to shower or wash your clothes in chlorinated water: You can buy at your own cost a filter that attaches to your water supply where it enters your property. It will remove all the chlorine from the water to your home.

The use of filters will reduce  any risks for those on dialysis. This can be arranged by the Canterbury District Health Board.

Chlorine can be an irritant for existing skin conditions 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 your 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 for free health advice on 0800 611 116.

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 a third of the water at a time. If you’re still worried, you can buy de-chlorinating kits (sodium thiosulfate) at pet supplies stores.

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 quality and thickness of the copper used.

Because of this, the Council will not be compensating property owners where cylinders fail.

In Christchurch, where there was an increase in hot water cylinders failing after the introduction of chlorination it appears the majority of the cylinders that failed were reported as older, low pressure copper cylinders.