Residents of Carterton are being told they should keep boiling their water while the district council tries to definitively work out the source of E-coli.
Photo: 123RF
A boil-water notice was issued on 12 March after low-level contamination was found in two bores, which supply the 4200 people on the network.
The council lifted the notice after three clear days but reissued it on Wednesday after another positive result.
It says the risk is extremely low and to date there have been no reports of illness.
Showering, hand-washing and shaving are fine with unboiled water as long as it's not swallowed.
Council contractors, regional public health experts, and external senior water engineers are working to identify the source somewhere in the town's system.
The council reported two other results of the bacteria in December and January.
On both occasions, council staffers locked down two water bores in town water supplies and increased chlorine treatments after testing returned elevated levels of the deadly bacteria.