Do you know more? Contact us.Latest tests on the town's water supply have revealed it is "highly likely" that the bug causing the illness is campylobactor.
Since the outbreak, the town's water supply has been chlorinated, boil water notices are in force and tankers of fresh water have been brought in.
Council water services manager Brett Chapman said ultraviolet treatment was proven to remove the contaminants that made people ill and was an additional level of treatment on top of chlorination.
Watercare staff would arrive tomorrow to check the site. The unit was expected working by the end of next week.
Until now, Havelock North's water supply had been deemed secure and no treatment was required.
However, because of the outbreak, permanent treatment would now be required.
Hawke's Bay District Health Board said two of the town's sickest patients were now recovering with one stable condition and moved to a general ward and the other critical but stable in Intensive Care.
Numbers affected by the outbreak admitted to hospital had dropped to 17 from 22 at the start of the week.
At the same time local doctors reported hundreds of sick people continuing to seek help with general practices treating 231 patients yesterday.
There were now 62 confirmed and 129 probable cases of campylobacter now reported.
The region's Medical Officer of Health Nick Jones urged people to be extremely vigilant about washing hands.
Anyone who worked in the food industry and was sick was asked not return to work for 48 hours.
