A water firm's "unclear" advice to up to 700,000 customers when their tap water became contaminated "caused uncertainty", a report has concluded.
United Utilities (UU) admitted supplying water unfit for humans after animal waste contaminated water with cryptosporidium at Franklaw treatment works near Preston in 2015.
The Drinking Water Inspectorate said the company did not specify "who it[the advice] applied to" during the outbreak, which left consumers "confused".
UU said it has been "implementing many of the recommendations" since 2015 and had shared its learning "across the water industry".