United Utilities has notified customers in parts of Lancashire that they can now drink their water without boiling it.
The firm said its work to remove the cryptosporidium bug from its systems was slowly working, and those in certain postcodes could now use water as normal.
But some customers are still being told to comply with a boil water request issued on 7 August.
United Utilities said earlier this month that its Franklaw treatment plant was clean but that a network of 4,000km of pipes and mains, and storage reservoirs holding 500M litres of water, had to be flushed out before the boiled water notice can be lifted in all areas.
Ultra violet rigs have been installed in certain parts of the network to help kill off the bug.
The firm said in a statement to customers yesterday: “We will continue our work to remove the bug from all parts of the Lancashire network and will lift the boil water notice in further areas as and when we are able to do so and will write to you when you no longer have to boil your water.
“If in doubt, please use our postcode checker to see if you are still affected.
“We all want things back to normal as quickly as possible and we’re continuing to liaise closely with the Drinking Water Inspectorate and Public Health England, and meeting with them regularly to review the very latest test results. We’re confident that the work we are doing is helping water quality to return to normal as quickly as possible.”