Investigations by the NFU have found that some of the new water retail companies are behind the mistake.

Tom Ormesher, NFU South East’s environment and land use adviser, explained that it is standard procedure for drinking troughs and septic tanks to be exempt from sewerage charges by a “non return to sewer” arrangement.

But since a new water retail market opened for business customers – including farms – earlier this year, things have begun to go wrong. In the Thames Water area, Castle Water took over management of all business customer accounts. However, its processing of agricultural account holders has not gone according to plan.

“In early October, we wrote to Castle Water to complain about the fact that our members are being charged for services they do not receive,” Mr Ormesher explained. Castle Water replied saying this should not have happened, and Thames Water has been asked to review all the accounts and ensure the charges are correct.

Castle Water’s statement continued: “Castle Water is paying wholesale charges to Thames Water for waste services on behalf of these customers, and we are therefore obliged to invoice.

“In some cases – for example where the first line of the address is ‘trough’ – it is quite obvious that there might be an issue. However, in a lot of cases the issue is not so easily identifiable from the supply address details provided by Thames. In almost all cases, until a customer brings it to our attention that they have a septic tank or that they have no need for wastewater services at all, we are not aware of this.”

When these accounts come to light, Castle Water said it places the account on hold to ensure it takes no action to pursue the sums invoiced. Thames Water is contacted to “deregister” the wastewater supply point and cancel the charges. Thames Water’s process for investigating and then cancelling the charges can take a number of weeks, Castle Water added.

Mr Ormesher added that any farmer affected should write to Castle Water quoting their customer account number. They should ask for their account to be put on hold and make sure Castle Water request that Thames Water deregister the wastewater supply point.

An independent consultant has told the NFU that there are 57,000 supply points in England and Wales for trough and field supplies, of which 1,348 are flagged for sewerage charges (two per cent of all trough/field supplies). Of these flagged supply points, 904 are within the Thames Water sewerage supply area (water suppliers are South East, Affinity, Southern, Sutton and East Surrey and Thames) and are billed primarily by Castle Water, as well as Business Stream. “They account for 10% of all trough/field supplies for those specific water companies listed, so the issue may be particularly extensive in our region,” said Mr Ormesher.