A small settlement in Taranaki is boiling its drinking water, after it was found to contain the E. coli bacteria.

Residents of Toko, about five kilometres east of Stratford, were notified of the contamination yesterday.

Stratford Council's Sven Hanne said they will need three days of clear testing before they can declare the water safe to drink again.

He said they are still unsure how the bacteria made it into the water.

"Given that the plant and the reservoir are both under a year old, we're obviously disappointed that this has happened."

He added that they were "trying to trace it back and get an indication of how it got in."

People who ingest the E. Coli bacteria can experience stomach cramps, diarrhea, vomiting and fever.