Chlorination FAQs

Chlorination is a requirement of water regulator Taumata Arowai which took responsibility for regulating drinking water from the Ministry of Health in 2021 under the Water Services Act.

Chlorine is used around the world to help make drinking water safe. It’s a safe, simple and inexpensive way to kill bacteria and waterborne diseases.

Chlorine kills bacteria such as campylobacter and norovirus that can get into water supplies and spread disease. It is used alongside other processes such as a protozoa barrier that removes cryptosporidium and giardia.

In New Zealand all public drinking water supplies are required to be chlorinated. Chlorination provides an additional safe, effective treatment and is used alongside other processes such as a protozoa barrier

For more information go to Taumata Arowai's website

Yes. Most drinking water supplies in New Zealand are chlorinated and chlorine is widely used to treat water supplies against contamination. The amount used is carefully managed to ensure the smallest amount is ingested while maintaining a high level of effectiveness.

You can 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.

Or you can buy an under-sink activated carbon (GAC) filter. These are available from hardware stores and water filter companies. If you don’t want to shower or wash your clothes in chlorinated water, you can buy a filter that attaches to your water supply where it enters your property.

The law requires a minimum dosage of 0.2 parts per million (ppm) in the water when it reaches each property on the supply which means some parts of the network will have up to 0.6ppm to ensure the level at the extreme edges remains at 0.2ppm.

Chlorine levels are carefully managed to ensure levels of chlorine in the water are safe.

As chlorine is introduced to a supply you may notice a slight taste as it begins to mix in. This will generally decrease with time and may take six to eight weeks for the system to settle down.

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

There are no known health impacts from drinking water treated with chlorine. The use of filters will mitigate any risks for those on dialysis. You can call your GP and ask the nurse for advice or contact Healthline for free health advice on 0800 611 116.

Chlorine can irritate skin conditions such as asthma or eczema. If you feel your skin getting dry or itchy, moisturise after having a shower or bath. If you notice increased skin irritation, asthma symptoms or other symptoms, seek medical advice from your GP.

The International Agency for Cancer Research does not believe chlorinated water is a probable or possible cause of cancer. The Journal of the National Cancer Institute acknowledges that “water chlorination is one of the major disease prevention achievements of the 20th century”.

Chlorinated water is safe for cats, dogs, birds and other mammals to drink but can be toxic to fish, reptiles and amphibians because they 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) or fill up drums of water and let them sit for at least 24 hours before using it.

For indoor fish tanks or bowls, fill 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.

Some readers may recall swimmers with blonde hair saying their hair turned green from regular use at public pools. That was in the day when heavier concentrations were perhaps used. Chlorine in a water supply will not have the same impact as a pool due to it having a much lower concentration.

Chlorination has been introduced to many water supplies throughout the years with no issues.

There are multiple factors that can lead to a hot water cylinder leaking and 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.

It appears most cylinders that fail are older, low-pressure copper cylinders.

Most plants are safe if residual chlorine concentrations are <100 ppm. We will be aiming for a residual concentration of 0.2 to 0.6 ppm. However, some floriculture crops are sensitive to chlorine. Chlorine has been added to the water supplies for Picton, Renwick and Havelock for many years and we are not aware it being detrimental in these locations.

Very high doses of chlorine can be harmful to septic tank but the level being used in Blenheim water supplies is too low to have an impact.