Thames Water has launched an online tool to help customers gain a better understanding of their water use and eventually save money.
The free calculator makes predictions based on responses to questions about how much water people use in their homes and gardens.
The answers allow customers to calculate their energy consumption such as heating up water for showers and baths and show how simple changes can help save money on bills.
With an estimated 2.1 million additional people expected to move into the Thames Water region over the next 25 years, Thames Water has predicted a shortfall of 350 million litres of water a day by 2045.
By 2100, this is forecast to increase to 650 million litres a day.
As part of its draft Â£11.7 billion business plan for 2020/25, it will offer free smarter home and business visits to more than 400,000 customers and install 700,000 domestic smart meters to put people in control of their water use.
Water Efficiency Manager Andrew Tucker said: â€œAlthough weâ€™ve previously had online calculators, the new one has been designed to reflect typical lifestyles and modern living based on feedback from our own customers. Itâ€™s also the first calculator of its kind to identify how much water a customer typically uses outside of their home, such as when showering at the gym. This gives everyone a better understanding of their real life daily water use.â€