It wreaked havoc across the Fylde coast for more than a month, and cost water bosses millions in compensation.
Last year, families and businesses throughout the county were warned to boil all drinking water after a microscopic bug posing a health risk was found in tap supplies.
Investigations are ongoing and we will be putting information into the public domain as soon as we are able to
But, 12 months after traces of cryptosporidium were first discovered, scientists are still unable to reveal how it got there.
An investigation was launched by the Drinking Water Inspectorate (DWI) into the contamination, but has still not reached a conclusion on what caused the major health scare.
A DWI spokesman said: “Investigations are ongoing and we will be putting information into the public domain as soon as we are able to.
“It’s a large and complex system and there are a number of lines of inquiry which need to be pursued to their conclusions.”
Bosses at Public Health England said they were also waiting for a report from the DWI, while water firm United Utilities added: “We are still cooperating with the Drinking Water Inspectorate’s ongoing investigation. The findings will be made public once the investigation is complete. The timing is a matter for DWI.”
It was on August 6, 2015 when more than 300,000 homes and businesses were first warned to boil all drinking water to protect against the nasty parasite.
The Fylde coast, Preston, South Ribble and Chorley were affected, and it took 30 days for all supplies to return to normal, leading to compensation payments of between £50 and £60 to all domestic consumers and much more to businesses affected by the alert.
A dead pheasant in an outflow pipe was the most popular theory as to the source.
When the investigation was launched, it centred on the United Utilities water treatment plant at Franklaw near Garstang.