E.coli levels are still increasing in Wellington water, as officials try to track down the source of the contamination.

Lower Hutt's water supply is being chlorinated, while artesian water wells in Petone and Dowse Square have been closed.

Officials said the safety precautions meant the water was still safe to drink.

The most recent water testing showed the amount of bacteria was increasing.

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November's Kaikoura earthquake is being put down as a possible cause of the contamination. However, the exact source hasn't been found.

Lower Hutt mayor Ray Wallace said there was no issue more important than the safety of drinking water.

"We know many residents really value access to unchlorinated aquifer water, but public safety will always be our number one priority.

"We're working together, taking a cautious but vigilant approach, and will continue to do so throughout the investigation."

In response to questions on his Facebook page, Wallace advised residents to put containers of chlorinated water in the fridge before drinking, to improve the taste.

He didn't respond to requests to remove fluoride from the water supply while the artesian wells were closed.

Wellington Water acting chief executive Mark Kinvig warned the situation wouldn't get a quick fix.

"The cause of the postive E.coli result and increased bacterial activity isn't known at this stage, but it may be related to the November 2016 earthquake.

"We're carrying out investigations into the source but this is expected to take many months to complete."

Greater Wellington Regional Council chair Chris Laidlaw said they weren't taking any chances with public health.

"We immediately chlorinated Lower Hutt's water supply in response to the recent positive E.coli test, and we'll continue to chlorinate while we investigate the source of the results.

Wellington Water has promised to investigate non-chemical treatment options that would allow the artesian water fountains to be re-opened to the public.