As many as 14,000 homes in the South East could be included within the boundaries of the experiment, which would be the biggest of its kind, The Telegraph reports.
It be an extension of a smaller trial carried out between 2023 and 2025 on 1,500 homes designed to encourage water-saving, which worked by providing an initial amount or “block” of water free, with charges escalating the more water is used.
The newspaper understands a fourth block targeting “very high users” is set to be introduced, resulting those with bigger homes and large families are likely to pay a higher rate.
Elsewhere, Portsmouth Water is developing two trials for households on smart meters for 2026-27 with the first allowing homes to “pre-pay” for a fixed amount of water based on their expected usage, at less than the current standard rate.
Other residents will be encouraged to cut their water usage with lower rates for those who undershoot expected consumption.
Britain’s biggest water company, Severn Trent, also began a “rising block tariff” trial in February, affecting 5,000 homes.
Anne Pardoe, at charity Citizens Advice, said: “Soaring water costs are already pushing people to the brink.
“We’ve seen the real harm poorly designed reforms can cause in other sectors, like energy, as more people seek support from our services.
“It’s essential that any changes to how people are charged for water, such as block pricing, are designed to protect – not penalise – consumers.
“Carefully designed safeguards must be implemented to avoid intensifying pressure on groups who have higher water needs, like families and disabled people.”
Affinity said it was “still analysing the water efficiency savings” of its initial block pricing trial, saying the results would be published later this year, adding that most customers had saved money.
Portsmouth Water claimed making its trials “fair and inclusive” was a priority and said: “We also believe it is essential to build in protections for customers who experience life changes that may affect their water usage.”
A spokesperson added: “Importantly, our approach is centred on rewarding positive behaviours rather than penalising customers.”