Thames Water wants to spend £11.7bn over the next five years, according to its business plan submitted to regulator Ofwat.
Water companies across the country submitted spending proposals for the 2020-25 period.
Midlands supplier Severn Trent pledged to spend £6.6bn over the next five years, with these funds largely invested in improving the ability of its water supplies to cope with shocks and strains, rather than on a major project.
North-west provider United Utilities tabled £5.4bn of expenditure, while Anglian Water said it would increase investment by 30 per cent to £6.5bn for 2020-25.
Ofwat said it would scrutinise the firm’s proposals and publish an initial assessment of each plan by January 2019.
Thames Water’s submission revealed a £2.1bn programme to improve resilience and reduce leakage in its infrastructure.
Its chief executive Steve Robertson said the plans included a strategic reservoir for the South-east.
Thames Water said its proposals would see “modest distributions” of £20m annually to its shareholders as it “prioritises investment” in its network.
It added that it would reduce its debt-to-equity position to 76.2 per cent and increase its equity buffer to £4.7bn in order to increase its financial resilience.
The company also plans to reduce operational unit costs by nearly 14 per cent and simplify its corporate structure.
Thames Water announced that, post-2020, its management bonuses and dividends would be tied to meeting targets on reducing leakage and pollutions, and increased customer satisfaction.
Mr Robertson said: “Our responsibilities to the environment and customers are huge, and we will partner with them and our peers to insulate our region from the effects of changing climate patterns.
“This includes planning for a strategic reservoir for the South-east region of England and exploring the potential of water transfers.”
Thames Water also said it was committing to an 18 per cent reduction in pollution incidents, cutting leakage by 15 per cent and creating enough green energy to power 115,000 homes.