Water provider United Utilities is being taken to court for the cryptosporidium incident in Lancashire almost two years ago.
The company has been ordered to appear before magistrates in Preston on June 30 charged with supplying contaminated water to around 300,000 homes and businesses across the county.
We have received a summons and a full court case will be heard in due course
The Drinking Water Inspectorate, which has been investigating the case since August 2015, has accused the firm of providing water from the Franklaw Treatment Plant near Garstang which was unfit for human consumption, failing to disinfect supplies and failing to operate an adequate treatment process at Franklaw.
The case follows an incident in which the microscopic parasite was discovered in a filter at Franklaw and blighted large parts of the county for up to a month.
In all an estimated 700,000 people were affected as United Utilities advised consumers to boil all water used for drinking and food preparation.
The contamination is estimated to have cost United Utilities around £25m in compensation, although not one confirmed case of illness due to cryptosporidium was officially reported.
Areas affected included the Fylde Coast, Preston, South Ribble, Chorley and parts of the Ribble Valley.
A spokesman for the company said: “We have received a summons from the Drinking Water Inspectorate and a full court case will now be heard in due course.
“United Utilities has taken a full and open role with the DWI during their investigation and complied with all requests.”