Concern for the safety of Sir Roy, who suffers from Parkinson's disease, has been mounting since he disappeared after his chauffeur dropped him off at his south-west London home on Tuesday afternoon.
A search of his Battersea flat has revealed that he did not have any credit cards, cash, medication or extra clothes with him. It is understood that Sir Roy, 67, had been depressed.
'We are very concerned about his welfare,' a spokeswoman at Thames Water said. She added that Sir Roy had been working at his office in London just before his driver took him home. Scotland Yard expressed similar concern and is appealing for anyone who has seen Sir Roy since Tuesday to contact the duty inspector at Battersea police station, on 071 350 1122. Sir Roy is described as balding with short grey hair, clean shaven and about 5 ft 9ins tall. He is believed to have been wearing dark grey trousers, a light blue shirt and a heavy cable-knit sweater when he disappeared.
Married with three children, Sir Roy served in the Royal Tank Regiment during the Second World War before becoming a local government accountant.
He then spent almost 30 years in the civil aviation industry, with British European Airways and then British Airways, where he became vice-chairman and introduced shuttle flights.
He became chairman of Thames Water in 1983 where he became the driving force behind the contentious move towards privatisation. He was determined to turn the statutory water authority into one of the largest companies in Britain.
Sir Roy has been criticised for taking large salary rises and share options from which he stands to make a considerable sum. He was knighted in the Queen's Birthday honours list last year.
Lady Watts said last night: 'My husband must be unwell to have done this. I'm terribly worried about him.'