Water chlorination is the process of adding chlorine to the water supply to keep it safe from harmful bacteria. Sodium Hypochlorite is used in Christchurch. It can be added as a precaution after routine work, such as reservoir cleaning, or as a result of finding bacteria in the water supply during routine water sampling.
The Christchurch water supply is made up of several zones that operate independently of each other. While the main city urban supply is being temporarily chlorinated, supplies for Akaroa, Duvauchelle, Little River and Takamatua are permanently chlorinated.
The well heads on the groundwater wells servicing our city are no longer deemed secure. Monitoring shows there is a very small risk of contamination entering the water supply through the well heads. We are temporarily chlorinating the water supply on the advice of public health professionals because chlorination provides an extra layer of protection, just in case.
Chlorine will need to be added into the water until the Council and public health officials are satisfied the below ground well heads across Christchurch are fully sealed so there is no risk of contamination.
The Council resolved that long-term it wants to retain the city's untreated water supply system and will oppose any Government moves to impose mandatory permanent chlorination.
Temporary treatment is expected to cost about $600,000 to set up and about $250,000 a year to run.
The chlorine might be noticeable at the beginning of the treatment process but the taste will become less noticeable the further away from the pump station you are. If you are concerned about the taste, you can keep drinking water in a jug in the fridge. The chlorine taste will dissipate naturally over a few hours.
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.
Chlorine and any associated by-products can removed by using a granulated activated carbon (GAC) filter. These are available from hardware supplies stores and water filter companies.
Health and safety
There is no health risk from drinking our tap water.
There will no need to make any changes to how you use water. There are no known health impacts from drinking water effectively treated with chlorine and it is safe for pregnant women to drink.
The amount of chlorine dosed into the water supply will be carefully managed to ensure levels of chlorine in the water people drink are absolutely minimised.
The use of filters will mitigate any risks for those on dialysis. This is being arranged by the Canterbury District Health Board.
In a small number of people chlorine can be an irritant for an existing condition 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.
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.