According to Greens Senator Bob Brown, letters containing the reports of results of testing of the local water supply sent to residents in Tasmania's northeast has created doubts.

ABC's Australian Story program had stated that the St Helens drinking water supply was toxic.

The Health Department, the Break O' Day Council and Ben Lomond Water sent letters to the residents, which stated that a negative result was returned after testing of water for chemicals from eucalyptus trees.

But according to Senator Brown detail about which chemicals were tested for was not mentioned in the letter.

He said, "Has Dr Taylor been able to assure himself and therefore the people that he's not missing a pathogen that hasn't been tested. That's the real question, is he giving the all clear, and if not, then when will we get the all clear."