Lower Hutt's water supply will continue to be chlorinated despite tests giving it the all clear. 

Hutt City Council said Naenae Reservoir tested positive for E. coli on Friday, but further testing has found no E. coli in the water.

Wellington Water spokesman Alex van Paassen said it's good news but they're remaining cautious.

"We'll be testing and chlorinating for another day, if those results come back all clear then that will give us three days all clear since that original positive sample."

Mr van Paassen said only then will experts consider reducing chlorine levels.

In the meantime, residents are being asked to conserve their water and seek medical help if they have vomiting or diarrhoea.