United Utilities say it is unlikely to lift its boil water notice until Friday, nine days after the company found traces of cryptosporidium in its water supply.
Around 300,000 residents in Lancashire are still being told to boil tap water before drinking it, preparing food and brushing teeth.
United Utilities told Granada Reports the situation is now 'in the hands of the scientists' at its laboratory in Warrington where tests of water samples for the water-based parasite are taking place around the clock.
On Monday, the company said one clear sample had been found overnight and it was hoped water would be safe to drink from the tap again by Wednesday this week.
To lift the boil water notice, scientists need to find three negative samples within 24 hours.
However today we are told small traces of cryptospordium remain in the water supply, and the current situation is unlikely to be resolved before the end of the working week.
Until that time, the boil water notice remains in place as a 'precaution' and the company insists the risk remains low and is 'getting lower'.