Urgent inspections have been carried out at nearly 20 other water treatment plants in Northern Ireland following the explosion that killed a man in Derry yesterday.
Father-of-six Drew Stevenson (51) was working as a welder on the roof when a storage tank was blasted through it 200 feet in the air.
His son, Barry (27), said: "My father was a decent and hard-working man. He lived for his family. It is hard coming to terms with what has happened."
Two workmen were injured in the accident at the waterworks close to the village of Eglinton, near Derry.
Police, fire and Health and Safety Executive investigations are continuing today into the cause of the blast.
At the height of the alert yesterday morning, people were urged to stay indoors because of fears of dangerous gases leaking. Politicians praised the response of the emergency services and called for a full and open inquiry into the accident.