30 Jul 2018

Here are the answers to some of the questions you might have about the Council's decision to temporarily treat the city's water supply.

  1. Why has the Council decided to temporarily treat the water supply with chlorine?
  2. What does the chlorine do?
  3. How safe is it?
  4. How much chlorine is needed to treat our water supplies?
  5. Will I be able to taste the chlorine?
  6. What other effects will chlorination have?
  7. Is the water safe to drink in the meantime?
  8. Has chlorine been used in Christchurch’s water supply previously?
  9. What is it going to cost to set up the temporary treatment?
  10. Can I have a bath, wash vegies and do the dishes with chlorinated water?
  11. Is chlorinated water safe for people with health issues and those on dialysis?
  12. I don’t want chlorinated water. Is there anything I can do?
  13. How come it’s not okay for us to drink untreated water from deep aquifers but it is okay to bottle and sell it overseas?
  14. For how long will our water need to be treated with chlorine?
  15. Why can’t we just treat the water with UV?
  16. What are the Drinking Water Standards? 
  17. What if I have a skin condition or sensitivity to chlorine?
  18. Will the water supplies going to communities in Lyttelton Harbour also be chlorinated?
  19. Can't the Council just turn off the wells that are a problem to avoid chlorination?
  20. What about my pet fish?
  21. Will you use chlorine, or chloramine (chloramine is more toxic to fish)?
  22. Once the wells are fixed and the chlorinating stops, how long does it take for the chlorine to dissipate?
  23. Will chlorination increase the release of lead from brass fittings, and will it change the frequency of replacement of sacrificial anodes in hot-water cylinders?
  24. Does chlorine cause cancer?

 

1. Why has the Council decided to temporarily treat the water supply with chlorine?

The well heads on the groundwater wells servicing our city are no longer deemed secure as there is a slight risk of contamination occurring through our infrastructure.

For groundwater supplies to be classified as secure, well heads must be impermeable so that surface water and ground water can’t get in. The below-ground well heads are not at that standard. We are working to upgrade them but completing that work will take some time.

In the meantime we received advice from health authorities that we need to chlorinate the water to provide an extra layer of protection.

A person takes a drink from a glass of water.

Christchurch's drinking water is going to be temporarily chlorinated for health reasons.

2. What does the chlorine do?

It kills the bacteria that can get into water supplies and spread disease, helping ensure supplies are safe to drink.

3. How safe is it?

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

4. How much chlorine is needed to treat our water supplies?

We have an agreement with the Drinking Water Assessor to dose at a rate of 1 part per million where we can achieve 60 seconds' contact time and 0.5 parts per million where there is two minutes' contact time. The contact time is determined by the length of time the chlorine is in water within the network before anyone draws it off to use.  

That maximum chlorine dose allowed is 5 parts per million under World Health Organisation guidelines and the Drinking Water Standards for New Zealand.

We are testing chlorine levels daily from different points in the system and adjusting the dose where needed. All test results are below the maximum set in the Drinking Water Standards.

We are not able to do individual samples at residents' properties on request.

5. Will I be able to taste the chlorine?

Initially when non chlorinated water supplies are chlorinated you will notice a stronger smell and taste.  This will reduce over time as the chlorine breaks down the biofilm which naturally occurs on the inside of the pipes. The effect will vary depending on where you live and what pump station you get your water from.

Our contractors will be flushing pipes in areas that report significant problems to help reduce the effect.

The taste and smell is something that towns and cities that have been chlorinating their water for some time will not experience to the same extent. This explains why people will notice a difference compared with places they have visited or previously lived. 

If you are concerned about the taste, you can keep drinking water in a jug in the fridge. Make sure you leave lids off containers so the chlorine can evaporate.

6. What other effects will chlorination have?

The chlorine may react with organic content in the pipes and dislodge it. That could result in some harmless organic matter coming through your taps after the initial treatment dose. The water should clear though once the tap has been run for a few minutes.

7. Is the water safe to drink in the meantime?

Yes, tap water is still safe for humans and pets to drink. The quality of the groundwater remains excellent and it is tested daily to ensure it is free of bacterial contaminants.

8. Has chlorine been used in Christchurch’s water supply previously?

Yes – intermittently. The Council put chlorine in the water immediately after the earthquakes. It also uses it when bacterial transgressions are detected. For example, a Diamond Harbour water reservoir was treated with chlorine just before Christmas because water sampling showed there was E.coli bacteria in the reservoir.

9. What is it going to cost to set up the temporary treatment?

Temporary chlorination has cost $2.3 million to install with an estimated annual operational cost of $1.1 million to treat and monitor the network, and maintain the temporary plant. 

10. Can I have a bath, wash vegies and do the dishes with chlorinated water?

Yes. There is no need to make any changes to how you use water.  

 

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.

To minimise exposure to chlorine, try bathing at times of low water demand – in the middle of day on weekdays, early in the morning (before 7.30am), or late in the evening (after 9.30pm).

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 for free health advice on 0800 611 116.

11. Is chlorinated water safe for people with health issues and those on dialysis?

There are no known health impacts from drinking water effectively treated with chlorine. The use of filters will mitigate any risks for those on dialysis. 

12. I don’t want chlorinated water. Is there anything I can do?

Chlorine and any associated by-products can be removed by using a granular activated carbon (GAC) filter. For fish tanks, sodium thiosulfate can be added at the prescribed dosage.

13. How come it’s not okay for us to drink untreated water from deep aquifers but it is okay to bottle and sell it overseas?

Most bottled water is treated with UV light. Decisions about water allocation are made by Environment Canterbury.

14. For how long will our water need to be treated with chlorine?

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.

15. Why can’t we just treat the water with UV?

Initially it was thought the cost would rule it out, however, now more is known about the extent of work required on the well heads, we are investigating if UV treatment is a suitable option in some instances.  

16. What are the Drinking Water Standards?

The Drinking Water Standards for New Zealand are issued by the Ministry of Health(external link) under the Health Act and set out the requirements water suppliers need to meet to provide safe water to their communities. The standards specify:

  • Maximum amounts of substances, organisms, contaminants and residues that may be present in drinking water.
  • Criteria for demonstrating compliance with standards.
  • Remedial action to be taken in the event of non-compliance with standards.

17. What if I have a skin condition 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. To minimise exposure to chlorine, try bathing at times of low water demand – in the middle of day on weekdays, early in the morning (before 7.30am), or late in the evening (after 9.30pm).

 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 for free health advice on 0800 611 116.

 

18. Will the water supplies going to communities in Lyttelton Harbour also be chlorinated?

Yes – the water for Lyttelton, Governors Bay and Diamond Harbour comes from Christchurch, so it will also be chlorinated. We will also be chlorinating the supply to Wainui.

19. Can't the Council just turn off the wells that are a problem to avoid chlorination?

No – more than two-thirds of the city's wells are affected and we would not be able to provide enough water to the city if we did this.

20. What about my pet fish?

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 1/3 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. Water treated with chlorine is safe for other pets such as cats and dogs.

21. Will you use chlorine, or chloramine (chloramine is more toxic to fish)?

We will use chlorine.

22. Once the wells are fixed and the chlorinating stops, how long does it take for the chlorine to dissipate?

It depends on where you live in the city. For residents on or near the hill suburbs, it would take up to a week for all the chlorine to be flushed from the network, as the water supply for this area comes from reservoirs. For every day that goes by, the concentration of chlorine will reduce as water fills the reservoirs. For residents that don’t receive their water from reservoirs, we would expect less than three days, maybe sooner.

23. Will chlorination increase the release of lead from brass fittings, and will it change the frequency of replacement of sacrificial anodes in hot-water cylinders?

You can find answers to your questions about hot water cylinders and how chlorination is effecting them here.(external link)

24. Does chlorine cause 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.

If you have any unanswered questions about the temporary chlorination, you can email them to watersupply@ccc.govt.nz.