Thames Water is owned by a consortium of institutional investors, predominantly large pension funds and sovereign wealth funds. The ownership is complex, involving intermediary companies, but the significant shareholders include:

• Ontario Municipal Employees Retirement System (OMERS), a Canadian pension fund, holding about 32%.
• Universities Superannuation Scheme (USS), a UK pension fund, holding around 20%.
• Infinity Investments, a subsidiary of the Abu Dhabi Investment Authority, holding about 10%.
• Other notable shareholders include British Columbia Investment Management Corporation (9%), Hermes Investment Management (9%), and the China Investment Corporation (9%).
• Smaller stakes are held by Queensland Investment Corporation and Aquila GP Inc.

The company was previously owned by Macquarie Capital Funds (2006-2017) and before that by RWE. Macquarie sold its shares, leaving Thames Water with substantial debt. Due to financial difficulties and debt exceeding £15 billion, there has been government consideration for temporary renationalization or restructuring of Thames Water.