Affinity Water has been sold to a three-member consortium that includes German insurer Allianz.
As part of the deal, the consortium will acquire a 90 per cent stake from co-owners of the water supplier, Morgan Stanley's infrastructure team and M&G Investments-owned Infracapital, for £687m.
The consortium will also acquire the remaining 10 per cent stake from French water and waste firm Veolia.
Both transactions are expected to complete in May 2017.
Simon Cocks, Affinity Water chief executive, said: "As a business we will continue to operate as normal, focused on achieving our strategic objective to become the leading community focused water company in the UK.
"We look forward to welcoming our new investors to the company and continuing to deliver our enhanced business plan for our customers."
Affinity Water’s profit before tax fell to £46m from £60m in 2015, while revenue rose to £303m from £296m in the same period, according to its financial results for the year ended 31 March 2016.