Water supply for most Christchurch homes has been chlorinated after potentially dangerous E.coli bacteria was discovered in the city's largest reservoir.
The E.coli was discovered during a regular test of the 37,000-cubic metre water reservoir on Huntsbury Avenue in St Martins on Thursday and chlorine was added on Friday.
The contamination meant two smaller reservoirs with a total capacity of 1465cu m of water had to be chlorinated.
Christchurch City Council pumps and control manager Graeme Black said the reservoirs supply water to most households south of Brougham Street all the way out to New Brighton.
Christchurch's water supply is untreated, but chlorine is added if regular council tests of reservoirs and pipes detect any bugs.
The Huntsbury contamination has been traced to rainwater leaking into the reservoir through a crack in the concrete tank. The crack was sealed yesterday morning.
Black said the reservoir had not been chlorinated since it was cleaned out four years ago and the contamination was "very, very rare".
"We have tested it every day and it has cleared any bugs that were in the system," he said.
The test found one E.coli microbe every 100 millilitres of water in the reservoir, so 0.5 parts of chlorine per million of water was added to clean out the supply.
Tap water would smell and taste slightly of chlorine until the reservoir is completely refreshed by Friday, said Black.
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