TRADING Standards are warning Hertfordshire businesses to be on their guard against cold callers.

The message follows a number of complaints from firms which have been visited by a representative of a company testing tap water in washrooms and staff kitchens.

Businesses targeted assumed that the engineers were from the council or water supplier and acting in an official capacity.

But, it is a commercial company and the engineers are cold calling.

They usually collect some water samples and then ask an employee to sign paperwork on their way out.

This is then followed by an invoice, often for �808, which relates to numerous tests carried out on the samples taken.

Guy Pratt, assistant director for community protection at Hertfordshire County Council, said: “It is not illegal to offer commercial water testing services to those who want it, but we are concerned that businesses felt misled and have not agreed to pay for this service.”