Chlorine is again being added to Napier's water supply following a positive E.coli reading - this time at the Otatara reservoir.

The chlorine free taps located at Tareha Reserve, Guppy Rd, have also been shut as a health precaution.

Chlorine has been added to the city's water supply twice this year after positive E.coli readings.

Today's decision was made following a low level reading for E.coli returned to Napier City Council.

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Although the level was at the very lowest limit of detection, a decision was made to commence chlorination of the reservoir, in conjunction with the Hawke's Bay District Health Board and Drinking Water Assessor.

Until today, the Otatara zone had remained unchlorinated, as hand dosing is required in order to treat the reservoir.

As part of a large programme of works instigated by Napier City Council following a series of transgressions, a new dosing system and pipework modifications servicing the Otatara zone will be in operation from December.

Hand dosing will continue in the interim, at least over the weekend.

Around 200 households are fed water from the reservoir.

"Again, we are taking all precautions available to us while we try to ascertain how E.coli has entered the Otatara reservoir," Director Infrastructure Jon Kingsford said.

"We have conducted testing at several points along the network services by Otatara and all results are negative for E.coli – so at least we know we are dealing with a contained area."

"One option we are exploring is to close off part of our network and isolate one of our bores – the T3 bore - which has never been chlorinated. However there is a real risk of water shortages and we're assessing whether this is viable during warm weather, with Otatara a high use area."

"Health remains our number one priority, hence the decision to chlorinate from today."