As well as striking down more than 5000 residents, and being New Zealand's largest outbreak of water-borne disease, the Havelock North gastro outbreak raised questions, and threw doubt on the security of drinking water - not just in Hastings, but across the country.

The future of how New Zealand's drinking water is treated is one of the questions the Government Inquiry looked at this week, expected to lead to improvements for how drinking water supplies are managed across the country.

Since the outbreak a year ago today, Hastings' supply has been chlorinated, with some sources receiving further treatment. Due to heightened awareness, Napier's supply has also received chlorination following two separate E. coli scares.

Ahead of the inquiry's recommendations, the Hastings District, and Napier City councils have started on mammoth work programmes to ensure they meet higher standards around drinking water.

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Hastings District Council

Since the outbreak, Hastings District Council has taken several steps to ensure the safety of its drinking water including increasing the range and frequency of testing across all supplies, lifting the bore heads above ground level, installing additional back-up power sources, and undertaking a full review of all of council's water-related processes.

Yesterday council chief executive Ross McLeod said they were expecting "to see the inquiry recommend a major overhaul of the Drinking Water Standards and other parts of the New Zealand drinking water regime".

"Expert panellists have highlighted the important role of treatment, including chlorine disinfection, in keeping communities safe.

"What happened to our residents last year was tragic and terrible, and we must do everything possible to make sure it cannot happen again," he said.

Work has already begun on a $12 million work programme, with the bulk of the project expected to be completed in about 24 months. This would involve shutting down Brookvale Bore 3 for good - bores 1 and 2 were closed down earlier this year.

The third bore would close after additional water could be supplied to Havelock North via a second mains pipe to be installed between the suburb and Hastings, and with the water take from existing Hastings bores increased where possible.

Under the proposed strategy all of council's urban water supplies would to be treated. The treatment plant put in place for Brookvale Bore 3 earlier this year would be relocated and used to treat other parts of the water supply.

"Ensuring our access to safe drinking water while improving the resilience and flexibility of our water supply system are at the very front of our considerations," acting mayor Sandra Hazlehurst said.

"We know that the treatment we have in place at Brookvale makes that water safe, but the impact of the bore on the environment means we must move away from that area."

The Brookvale bores had to be decommissioned as - aside from their transgressions - their consent was due to expire in May 2018, and their take was affecting the nearby Mangateretere stream.

So, council would be working to identify potential new water sources - the location was most likely to be within the wider Tomoana area. Work on a new bore field would be advanced, with preliminary investigations on potential sites.

Other new source locations being considered were Thompsons Rd, Whakatu, and Omahu Rd. Further investigations would be required before a final site could be decided upon.

Napier City Council

Given the high number of recent transgressions, work is also under way in Napier, where the water supply is in its third month of chlorination.

Late last month it was agreed the supply would remain chlorinated for at least three more months - particularly since the drinking water assessors have revoked NCC's secure bore status.

When asked if there was any indication if the chlorination could continue past this timeframe, council manager asset strategy Chris Dolley said once their maintenance was completed, they would like to ease chlorination and return to an untreated supply.

However this would have to be decided alongside the Hawke's Bay District Health Board, and the Drinking Water Assessor.

"Secure bores provide a barrier to contamination and with this status currently suspended it is a requirement to provide an alternative barrier - chlorination," he said.

"Chlorine is a treatment that is well understood, inexpensive and effective in its implementation. When secure bore status is reinstated and that barrier is in place, chlorination can be removed."

The council's "comprehensive" programme of work would look at operations, maintenance and capital improvements, and would take several years to deliver in full.

The council has earmarked half a million dollars for improvements to its water network, "to costs associated with changing industry expectation around public water supplies following the Havelock North Government Inquiry".

The council's list of network improvements is long - it includes the creation of a new drinking water quality manager role, seasonal water age testing with GNS to understand any seasonal impact on water age, and creation of a new water network model to facilitate improved infrastructure planning.

As well as this, council is planning several capital improvements including bringing the bore head works of seven of the existing bores above ground, improved reservoir security and fencing, and procurement of improved emergency treatment equipment.

What would not be considered was UV treatment - Mr Dolley said although the water was sourced from a confined aquifer, it was the carrying of this water to a consumer's tap where the potential for risks lay.

At this stage the council was also not considering any new water sources.

"Napier's water source is both plentiful and of a high quality," Mr Dolley said.

"At this point there are no plans to provide a different or alternate water source."

He added that as Napier grew, there would be a requirement to expand the source capacity, and additional bores would be required.

Hawke's Bay Today requested how much Napier's February, and current chlorinations had cost, but these figures could not be provided in the timeframe.