Chlorine in NZ tap water: what it does to hair, skin and nails

Chlorine became the law in 2022. But what does it do to your hair, skin and nails?

By the Kiri10™ Wellness Desk. Checked against the sources listed at the end. Updated 14 October 2026.

If you live in Christchurch, Napier, Hastings, Mosgiel, Geraldine or a long list of smaller towns, you can probably remember the week the chlorine started, because the water tasted of the public pool for a month and then you stopped noticing. If you live in Auckland, Wellington or Hamilton it has been there so long that nobody noticed at all. Either way, since November 2022 it has been the law: every piped water supply in New Zealand must carry a residual of chlorine through the network, at least 0.2 milligrams in every litre, unless the regulator grants an exemption. So far it has granted one, for 331 people at Rakaia Huts.

Why the chlorine is there, and why it is staying

In August 2016 about 5,500 of Havelock North's 14,000 residents fell ill with campylobacter after sheep faeces washed into an untreated bore. Forty-five people went to hospital and the inquiry found the outbreak may have contributed to four deaths. The inquiry recommended universal treatment of drinking water and a dedicated regulator. Both happened. The Water Services Act 2021 created Taumata Arowai, and from November 2022 residual disinfection became mandatory for every reticulated supply.

We want to be straight about this. Chlorine is the reason New Zealand will not have another Havelock North, and the World Health Organization is blunt that the risks from chlorine by-products are extremely small next to the risk of not disinfecting. Nothing in this article argues with that. The question is a different one: what does a lifetime of low-dose chlorine do to the protein your hair, skin and nails are made of, and what, if anything, is worth doing about it.

Christchurch tried hardest to say no. The city sat on five aquifers and 142 bores and had the best-tasting water in the country until the well heads failed a security audit in early 2018. Temporary chlorination started in March. Within a month the council had logged about 300 calls, a pharmacy in the central city reported a sudden run of people asking about eczema and dermatitis, and the mayor asked staff to lower the dose. In November 2023 the regulator declined the city's exemption applications, and chlorine went to every zone. In May 2025 the regulator's chief executive told councillors that chlorination must continue even though a virus study had found the groundwater clean, because the risk is in the pipes: Christchurch loses about a fifth of its water to leaks. A council workshop this April put a chlorine-free future at twenty years and $1.3 to $1.6 billion.

What is actually in the tap

The legal floor is 0.2 mg/L of free chlorine, measured in the network, and the legal ceiling is 5. Between those, every council sets its own dose. The regulator's own guidance says most people can taste or smell chlorine somewhere between 0.3 and 1.0, and adds that disinfection must not be compromised to avoid complaints. So several councils run inside that window on purpose.

The figures councils publish are patchy, which is part of why we charted them. Hamilton's city zone averaged 0.60 mg/L across 638 samples in 2020/21, with a high of 1.46. Wellington Water adds 0.6 to 0.8 at its plants and says 0.3 to 0.6 is the acceptable range at the tap. Kāpiti sends water out of its plants at 1.0 to 1.2. Dunedin's 2023 field readings ran from about 0.5 in the central zones to 1.2 at the Mt Grand reservoirs. Christchurch doses most of the city at 0.2, but 0.5 or 1.0 at pump stations where the first house is within a minute or two of the pump. Auckland, the largest supply in the country, publishes its compliance rate but not a typical level.

Two things stand out. The gap between towns is about six-fold. And in most of the country, you have no easy way to know where you sit, because the number is a dose at the plant, a target in the network, or not published at all. That is why we built the checker above.

What chlorine does to keratin, in plain words

Hair is more than ninety per cent protein, nearly all of it keratin. What makes keratin strong is sulfur: pairs of amino acids bonded across the protein chains. Hair keratin is unusually rich in those bonds, and the hardest outer layer of each strand, the cuticle, has the most. Nails are built the same way, which is why they are hard. The outer skin is keratin-filled cells packed in a fatty mortar.

Hair: what swimmers tell us

The clearest human evidence comes from people who get a lot of chlorine. In 2000 a Japanese dermatology team compared 67 members of the national swimming team with 54 people of the same age who did not swim. Sixty-one per cent of the swimmers had visibly changed hair; none of the non-swimmers did. Under the electron microscope, the swimmers' hairs had lost their cuticle entirely. Their hair contained less sulfur. And chlorine was found inside the strand, past the cuticle, in the pigment granules.

Skin: the one controlled experiment

The most useful study for tap water is small and precise. Twenty people with eczema-prone skin and ten without soaked their forearms for ten minutes in 40°C water carrying 0, 0.5, 1.0 or 2.0 mg/L of free chlorine. In the eczema-prone skin, the outer layer's ability to hold water fell from 0.5 mg/L upward. In normal skin the same change appeared only at 2.0.

We should also say what the evidence does not show. Big population studies linking home water to eczema in children have mostly found an effect of hardness, meaning calcium, not chlorine, and the one that separated the two called chlorine's independent effect uncertain. Chlorine does not cause eczema. The fair summary is that at the levels several New Zealand councils use, it can dry skin that is already prone to dryness.

Showers and baths: where the water actually meets you

When a US government team put volunteers through a ten-minute shower, a ten-minute bath, or a litre of the same tap water drunk over ten minutes, the highest blood levels of chlorine by-products were in the people who showered and the lowest were in the people who drank. A modelling study put the split for a ten-minute shower at roughly 30 per cent drinking, 40 per cent breathing and 30 per cent skin, shifting to 10, 70 and 20 for a twenty-minute shower. About 56 per cent of the chloroform in shower water ends up in the air of the shower. And heat matters: a bath at 40°C released about 35 times the chloroform of one at 30°C.

Drinking it: what we will not claim

You will find articles saying that drinking chlorinated water strips keratin from the inside, upsets the gut and so thins the hair. We looked for the evidence and there is none. Free chlorine is used up on contact with organic matter in the mouth and gut; it does not circulate to reach a follicle or a nail bed. The one good human trial, in 130 children a year after their water was chlorinated, found no effect on overall gut diversity. The World Health Organization's guideline for chlorine in drinking water is 5 mg/L, and most supplies sit at 0.2 to 1. Drink the tap water. It is the shower that touches keratin.

Where Kiri10™ fits in

Kiri10™ exists because our founder, Natalie, lost a frightening amount of hair after a period of chronic stress and could not find anything that was built around the protein hair is actually made of. She found Functional Keratin™, a soluble keratin extracted from New Zealand sheep's wool that keeps its natural structure, and built the brand she wished had existed.

KiriGlow™ capsules carry Functional Keratin™, 91% bio-matched to your own keratin, alongside hydrolysed marine collagen, OptiMSM™, biotin, zinc and copper, to feed the follicle from within. KiriCare™ shampoo, conditioner and serum put the same keratin on the lengths, where they strengthen, smooth, add shine and mean less breakage from styling. Both are made in New Zealand and 99% and 97% naturally derived. We ask for three to six months or more, because hair is slow and we would rather tell you that now than leave you guessing.

We are not going to tell you that any of it reverses chlorine damage or treats anything. It does not change the water and it is not a treatment. It is a daily keratin habit for the part of the story you control: the hair that grows in next, and the lengths you have while it does.