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  • Water Quality

    Information about our water quality and our means of compliance and advice on protecting our water supply

Ensuring safer water - chlorination

Under the Water Services Act 2021 (passed in November 2021), all councils must provide residual disinfection (chlorine) for all public drinking water supplies, unless an exemption from chlorination is granted by the drinking water regulator, Taumata Arowai.

Chlorination is widely and safely used in New Zealand and around the world for both short-term and permanent treatment to ensure protection against contamination.

The Council has made a major investment in recent years to upgrade its water supplies to have a multi-barrier approach using filtration, UV treatment and other barriers at all our water treatment plants. The required chlorination provides protection for water within the reticulation system (pipes and storage tanks) between the treatment plant and peoples taps.

In response to the requirements under the Water Services Act, the Council has chlorinated all its water supplies. Following consultation as part of the Long-Term Plan 2021-2031, the Council indicated that we would work with Taumata Arowai to clarify the requirements for gaining an exemption and consider the costs and rating options for upgrades to gain exemptions for our supplies.

Exemption applications

Selwyn was the first council in the country to file for an exemption from chlorination. This application was for an exemption for the Rakaia Huts water supply.

The Council's initial application for an exemption was declined in April 2023. Following further work in February 2024, Taumata Arowai granted  [PDF, 81 KB] the Council an exemption from chlorination for the Rakaia Huts water supply, subject to further conditions being met.

Based on the requirements for the Rakaia Huts, the Council estimated that meeting the requirements to remove chlorine from the majority of our supplies would cost $82.6 million and the ongoing cost if an exemption was granted for a scheme would be an additional $231 per year on the existing targeted rate for affected ratepayers.

Due to the impact on our ability to deliver safe water and the significant cost to upgrade our infrastructure, the Council decided in the Long-Term Plan 2024-2034 to continue chlorinating our supplies (including Rakaia Huts) and not to apply for further chlorine exemptions.

Frequently asked questions

Why is Selwyn water chlorinated?

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

In New Zealand all public drinking water supplies are required to be chlorinated under the Water Services Act 2021.

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

Chlorine levels are monitored continuously at our treatment plants and within the distribution to ensure the levels are safe.

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

How much chlorine is used in Selwyn's water?

The law requires that there is 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 put into the water supply is carefully managed to ensure levels of chlorine in the water people drink are safe. This dosage may vary at specific times if it is needed to keep your drinking water safe.

 I can taste/smell the chlorine, why?

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 the chlorine 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.

Why can I taste the chlorine more in my cup of tea?

Chlorine can react with lime scale or other deposit build ups in a kettle. The plastic parts in your kettle can also react with chlorine. In both cases this usually settles down pretty quickly - however, if it persists you may want to replace the kettle.

You can quickly test if the chlorine is reacting with your kettle by boiling the water in a saucepan to see if the taste is still there.

How do I remove chlorine if I don't want it in my water?

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 after 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 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. The filter 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 Health New Zealand.

What about skin conditions or sensitivity to chlorine?

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.

Is there an effect for pets?

Water treated with chlorine is safe for cats, dogs, birds and other mammals to drink.

Chlorine can be toxic to fish, other aquatic animals, reptiles, and amphibians. That’s because unlike other household pets, these animals absorb water directly into their blood stream.

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 it (the UV of the sun evaporates chlorine).

For indoor fish tanks or bowls, 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) from a pet store.

Will chlorine affect my pipes or hot water cylinder?

There are many things that can lead to pipes or a hot water cylinder leaking and needing to be replaced. These include (but are not limited to):

  • the chemical composition of the water
  • the age of the cylinder or pipes
  • the materials they are made out of and the quality of the materials
  • whether there is any debris in the cylinder or pipes.

Because of this, the Council does not compensate property owners for leaks.

What are the drinking water standards and the Drinking Water Quality Assurance Rules?

The Water Services (Drinking Water Standards for New Zealand) Regulations 2022 are issued by Taumata Arowai under the Water Services Act 2021 and set out the requirements that water suppliers need to meet to provide safe water to their communities. The standards set out:

  • Maximum amounts of substances, organisms, contaminants and residues allowed in drinking water.

The Drinking Water Quality Assurance Rules are compliance rules issued by Taumata Arowai under the Water Services Act 2021. The rules provide the minimum compliance requirements to ensure the drinking water complies with the Water Services (Drinking Water Standards for New Zealand) Regulations 2022.