The drinking water scare affecting around 300,000 homes in Lancashire may remain in force for at least two more days.
United Utilities say they are making significant progress in eliminating traces of the bug cryptosporidion in supplies.
One clear sample has now been tested, but scientists want to see a series of similar results before they can lift the alert across areas of the county including Preston, South Ribble, Chorley, the Fylde Coast and parts of Blackburn.
The parasite, which can cause stomach cramps and diarrhoea, was found in routine samples taken last week at the Franklaw Water Treatment Plant near Garstang on Thursday.
Residents were immediately warned to boil all drinking water and the scare has continued since then.
“we are hoping to get some positive updates in the next couple of days,” said a company spokesperson on Monday.
“We are getting some results that contain much, much lower levels and others that are clear. But we need to get a full set of tests that are clear. Hopefully that could be Wednesday or Thursday.”
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