UPDATED 1.01pm Test results have confirmed an elderly woman who died last week in Havelock North had contracted campylobacter.

Further testing is being done to determine what strain the 89-year-old had.

However, the Coroner has opened an investigation to see if the infection contributed to her death.

The Coroner said it's not clear yet if that is the case.

A post-mortem examination revealed she also had other significant underlying health issues.

Coroner Peter Ryan stressed that on the information currently available it is unclear what effect, if any, the campylobacter infection had on the woman's death.  This will be a focus of his coronial investigation.

Health officials have ramped up the number of people struck down by gastro troubles to more than 4000.

But the local district health board said the pressure on the health system is starting to wane.

Two patients are in intensive care.

Hastings Mayor Lawrence Yule has confirmed the tanker at Havelock North High School which returned a positive test for e-coli yesterday, has returned a negative test today.

He said this means the positive test was a false positive, and the water in the tanker was never contaminated.

Water tankers will be pulled from Havelock North streets this afternoon, so testing can be done to ensure they're clear of bugs and contaminants.

Hastings District Council has been supplying nine tankers to the township since Monday.

Mr Yule said the tankers will be removed from their sites at 4pm today, for re-sterilisation, and refilling from a secure source - under the supervision of District Health Board staff.

He said the tankers will then be tested, and won't be returned until the test results come back clear.

Boarding schools will receive bottled water from the council for the weekend.

Public Health Association chief executive Warren Lindberg said access to clean drinking water is taken for granted in New Zealand.

He said healthcare workers in Hawke's Bay are doing tireless work dealing with a outbreak that raises much wider questions for the country as a whole.

"We've just relied on the fact that in most parts of New Zealand you can turn on the tap and drink the water. And for it to go as wrong as this it is something we all should be seriously concerned about."

Mr Lindberg said families, businesses and schools have all been severely affected by the outbreak.

The Countdown in Hastings at the corner of Queen Street West and King Street North will be giving away free water this afternoon.

It'll be giving a box of 12 1.5-litre bottles to each household that comes forward, the supermarket says it has 500 boxes to hand out.