As work goes on around the clock to eradicate the cryptosporidium parasite from supplies in Preston, South Ribble, Chorley, the Fylde Coast and parts of Blackburn, scientists are carrying out extensive tests to establish if purification systems at the Franklaw Treatment Plant near Garstang failed last week, causing the parasite to leak into the mains.
United Utilities have 1,000 staff working on the alert, which has led to householders being warned to boil drinking water since Thursday.
As the scare entered its fifth day today, one of the Warrington-based scientists who discovered the contamination revealed it had been the first of its kind in the North West for at least 15 years.
“This is very, very unusual,” said Jeanette Williams, the company’s analytical technical manager as the investigation continued, “It was just trace levels. But we could be looking at a few more days yet before the system is fully flushed through and we can say it is OK to drink the water again.
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“Animal guts contain this bug, so that is the most probable source.”
United Utilities added investigations into the cause are ongoing and will be subject to a formal report from its regulator the Drinking Water Inspectorate.
Dr Kate Brierley, from Public Health England, added: “Until this is cleared up we would urge everyone in the affected areas to continue boiling their water.
“Cryptosporidium can cause an unpleasant illness which can cause watery diarrhoea which can last for a few days.
“There have been no clinical cases (of illness) confirmed to date. But obviously we are in a timeline where there maybe infections that occur in the next few days. That is obviously something we will be looking out for.”
United Utilities’ media spokesperson Helen Apps said: “Everyone in the company is devastated this has happened.”