Christchurch water as good as ever

31 March 2008

The application of new criteria for assessing the risk of contamination to public water supplies does not change the fact Christchurch has some of the best drinking water of any city in the World.

The assurance from the Christchurch City Council follows the release by the Ministry of Health of new figures measuring the risk of water contamination. Using a new definition of groundwater security, the assessment has resulted in a risk grading for Nor West Christchurch of Da, and a rating of Ba for the remainder of the urban City.

The “little a” grading refers to the quality of our water reticulation infrastructure and the management of this by the Council. The large “B” or “D” grading refers to the risks associated with the source of the water.

Ba is the highest risk grading the City’s water supply can receive without treatment.

“The bottom line is that Christchurch water is safe to drink,” says City Water and Waste Unit Manager Mark Christison.

“Today’s water supply is the same water supply we’ve always used. The only difference is how the risk is defined and assessed. The revised assessment tools are important however as they are used by the Council to target investment to ensure our residents continue to enjoy an untreated water supply,” says Mark Christison.

This is the first time that criteria set in the Drinking-Water Standards for New Zealand 2005 has been applied to Christchurch. According to this criteria, the risk of water supply contamination is based on how long water has been in the aquifers, and how secure those aquifers are from ground water contamination. 

The topmost aquifer in North West Christchurch is relatively shallow and does not have an impermeable confining layer above the aquifer storage area.  According to the Ministry of Health’s revised risk assessment criteria, this means this aquifer has a higher risk of contamination as the water is considered ‘young’ and ‘non-secure’.

“The only way to receive a higher grade for the North West zone would be to treat water from this aquifer and/or sink deeper wells in this area to draw water from deeper confined aquifers. Christchurch prides itself on not treating it’s water and the Council has no plans to introduce treatment,” says Mark Christison.

“Christchurch water is safe to drink and there is no need for residents to be alarmed. Our water is frequently sampled and on the very rare occasions where contamination is detected, appropriate corrective action is taken,” says Mark Christison.

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