Kemble Water is itself owned by a consortium of investors led by Australian bank Macquarie.
News of the acquisition follows Chancellor of the Exchequer George Osborne’s visit to the Far East this week, which included Hong Kong, Beijing and Tokyo, where he called for more investment by Asian companies in UK infrastructure.
The acquisition is the first to be made by the fund in the UK, which was established in 2007 to invest some of China's $3.18tn (£2tn) in foreign exchange reserves.
A one-line statement on the CIC website simply says that the Corporation has acquired an 8.68% stake in Thames Water with no purchase price disclosed.
A similar sale of 9.9% of Kemble Water was made in December to the Abu Dhabi Investment Authority sovereign wealth fund, again for an undisclosed price.