Ms Westcott said issues were caused by naturally occurring algae in the waterways that multiplied in warm weather when flows were low. "In Raetihi's case the alternative water supply we are using from the Makara Stream is smaller than the Makotuku River which was contaminated.
"The ecology of the stream will affect the taste, odour and clarity of the water with the smaller size and slightly different characteristics of the Makara tending to amplify any effects."
The council and its water contractor Veolia are closely monitoring the flow levels of the Makara. "Council and Veolia are working on some ideas to better monitor and control the Raetihi supply to provide greater protection for the town's water supply," Ms Westcott said.
She added: "At any time people can get ill with things such as rotavirus which is the leading cause of gastro-enteritis in young children, with symptoms such as diarrhoea, dehydration and vomiting.
"When people get sick they naturally look for a cause and some people with gastroenteritis have wrongly attributed their sickness to the water supply."