The Hawke's Bay District Health Board is yet to confirm whether the contaminated Havelock North water contributed to the death of a retirement home resident.
On Saturday the DHB chief executive Kevin Snee said a person had died, but could not confirm the death was caused by drinking contaminated water.
"We've seen eight quite unwell patients in one residential care home, and we've also, over the last 24 hours, had a death in a nursing home which may or may not be related to this problem, but is the consequence of a gastric-like illness."
Hastings mayor Lawrence Yule said the source of the gastroenteritis the person had was unclear because there had been outbreaks of airborne disease that could have caused it.
One person remains in the intensive care unit at Hawke's Bay Hospital but the other person who was admitted to the unit was no longer there.
Heather Grant, 26, said being a solo mother of two children under five meant it took a lot to knock her down, and this gastro bug had the oomph to do just that. The Hastings woman said she had no idea which water she drank that made her so sick.
"I drink water everywhere, I drink it at work, I fill it up at Te Mata Peak when I go walking."
Ms Grant had to enlist her grandparents to look after her children because the bug had drained all of her energy.
"It hit me over the weekend, Friday night and Saturday morning. I stayed in bed the whole weekend." She said it was by far the worst bug she had ever had, "I usually won't let anything get me down. It was pretty hefty, I couldn't do anything."
Ms Grant did not visit the doctor because she "figured out pretty fast" what was causing the diarrhoea and vomiting, the aches and pains, lack of energy and fever.
Yesterday Hastings District Council informed people a tanker supplying "safe" drinking water had indicated a marker for E.coli bacteria. Ms Grant said it was "ridiculous".
"I don't know how any one could've got it so wrong. There are no words to describe how dumb it was."