The death of a man who drowned after falling into a filtration tank in the course of his job was "an accident waiting to happen", a judge has said.
Robert Geach, 54, drowned when he fell into a sand filtration tank at a water treatment plant in Falmouth, Cornwall in December 2013.
South West Water has been fined £1.8m at Truro Crown Court.
The company previously pleaded guilty to failing to ensure the health and safety of employees.
Mr Geach was working alone when he attempted to fix a fault with the tank at the site on Falmouth Docks.
He removed a grill on the tank, and had to lean inside to unblock a filter.
He fell through the hole, and was found face down in 6.5ft (2m) of water.
The court heard how Mr Geach had activated the company's lone worker alarm system, but a slow response meant he was not found for four and a half hours.
In sentencing, Judge Robert Linford told Truro Crown Court the company had been warned of the potential risks previously.
He said: "The dangers of falling into tanks was pointed out to South West Water on a number of occasions, and the fact that something needed to be done."
He continued: "No correct risk assessment for the procedure had been done. This was an accident waiting to happen."
Dr Stephen Bird, Managing Director of South West Water said: "Robert was a valued colleague and we very much regret the devastating loss to his family and friends.
"South West Water has tried to ensure it learns all that it can from this incident."
The court heard how a new 'cat-flap' style grill had been introduced within four weeks of the accident, and that a new lone worker protection system is in place.