Charlotte Holland’s letter of May 17 about a “hidden water price hike” by Southern Water raises questions about our application of assessed charges. It might help affected readers if I explain: We are installing water meters for 92% of households across Sussex, Kent and Hampshire to help secure future water resources.

The remaining 8% of households will not be metered under our five-year metering programme. This is largely because these properties have complex plumbing systems or they share a supply pipe with other homes.

Households that cannot have a water meter will be switched to an assessed charge. This is a fixed charge based on the number of bedrooms in the property.

For example, a property with two bedrooms will pay an annual charge of £152.07 for fresh water and, if we also supply wastewater services, we will charge an additional £274.77.

However, customers who cannot have a water meter and live alone may be eligible for the single occupier tariff. On this tariff the customer will pay the reduced rate of £104.03 for fresh water and, if they receive wastewater services from us, an additional £190.67.

Customers who do not currently have a water meter will continue to pay their bills based on the rateable value of their property until their water meter is installed.

Rateable values were set by local authorities to reflect the rental value of the property. However, rateable values have not been revised since their abolition in 1990, which means they do not reflect any changes to a property or the local area.

There is strong evidence that charging households based on the number of bedrooms in the property is a good way to link the charges to the likely water use in the property. For that reason, the assessed charge is an approach used across the industry, where a property cannot be metered. It is cost-reflective and fairer than rateable value charges.

However, to support households who have seen an increase in their bill since being moved from rateable value charges to assessed charges, we will delay the switch until the following April 1.

We will also automatically place the customer on the changeover tariff, which phases-in the price rise over a two-year period giving customers time to adjust.

We have schemes to support customers in financial hardship. If you are struggling to pay your bill, contact our debt advice team.

Darren Bentham, chief customer officer, Southern Water