Artesian water wells in Lower Hutt have been closed and the city's water supply will continue to be chlorinated while officials investigate increased bacterial activity.
November's Kaikoura earthquake has been identified as a possible cause for the problem.
The fountains in Petone's Buick Street and Dowse Square - popular spots for locals to collect untreated water - are closed as a precaution because they cannot be chlorinated.
Officials are playing down the risk to the public and say tap water is still safe to drink.
They have been chlorinating the water supply since positive E.coli tests in the Waiwhetu aquifer from last week.