A leading clinical nutritionist based in Havelock North says there can be long-term health risks associated with drinking chlorinated water.
Havelock North and Hastings will have chlorinated water for at least three months, after the campylobacter outbreak which affected more than 4700 people.
Five remain in hospital, and one is in intensive care with the illness.
Permanent chlorination could be one option considered by authorities, as an in-depth Government investigation tries to find the source of the bug.
Be Pure founder Ben Warren said studies had shown what long-term use of chlorinated water could do to people's health. Long-term consumption of chlorinated water has been linked to cancers - primarily in the bladder, urinary tract and bowel.