His decomposed body was spotted 50 yards downriver of Westminster Bridge, by the crew of a passing barge.
Sir Roy, 67, who had been diagnosed as suffering from Parkinson's disease, was last seen by his chauffeur who left him outside his luxury riverside flat in Battersea, south-west London, on Tuesday of last week.
He leaves a widow, Jean, son Simon, 39, and daughters Sally, 37, and Anne, 41.
Sir Roy achieved national prominence riding out a storm over the disclosure that his salary had more than doubled - from pounds 73,000 to pounds 160,000 - following water privatisation.
'My job is to lead a company which produces results,' he told his critics at the time. 'We have to attract and retain good people. I hope you will agree that I have done a good job.'
He started his career as a local government accountant before joining British European Airways in 1955. He became its chairman and chief executive in 1974.
By 1980 he was British Airways' deputy chairman and chief executive. He joined Thames Water in 1983. He was knighted in June 1992.
An inquest is due to open today at Poplar coroner's court, east London.
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