Image source, PA MediaThames Water is seeking to persuade the regulator to let it raise consumer bills by at least 40% by investing more money in environmental projects.
The heavily-indebted water firm plans to spend an extra £1.1bn between 2025 and 2030.
Industry regulator Ofwat had dismissed the company's original plan, leading to questions over the company's future.
The firm's huge debts have led to speculation it could be taken over by the government.
Thames had originally proposed investing £18.6bn, but also increasing customer bills by 40% excluding inflation over the five-year period.
Ofwat dismissed this proposal, prompting shareholders at Thames' parent company, Kemble Water, to withdraw a proposed cash injection and default on debt interest payments.
Thames has now proposed spending an extra £1.1bn on top of its original plans on "projects benefiting the environment".
In addition, Thames said it could potentially increase investment by another £1.9bn, although that would lead to customers' bills rising by 44%.
It is thought that a final decision from Ofwat will come at a crucial meeting on 23 May with a "draft determination" of what companies will be allowed to charge from next year issued on 12 June.
Thames Water's operating company has reassured its 16 million customers it has enough money in the bank to continue delivering water and waste services until May of next year.
Thames Water chief executive Chris Weston said: "Our business plan focuses on our customers' priorities… we've now updated it to deliver more projects that will benefit the environment.
"We will continue to discuss this with our regulators and stakeholders."