It is believed that the cause is likely to be the tanker, however as a "super precautionary approach" the water supplies for Hastings and Flaxmere are now being chlorinated. The daily tests for those supplies have been clear.
While no boil water notice has been issued, as a precautionary approach, Mr Yule said people may want to boil any drinking water or use bottled water while the chlorine works its way through the system.
He said the test was an indicator, but the council had decided to make the information public.
"We will know the full results tomorrow. Seventy per cent of these test come back negative, but we have decided as a precaution to chlorinate the Hastings water supply."