There are fears that residents, particularly the elderly, are at risk of being electrocuted following the upgrade of water mains in Harpenden.

Affinity Water is replacing old iron mains with new plastic pipes at Crabtree Lane and Dalkeith Road until the first week of March.

But retired engineer and occupational psychologist Bernard Stewart, of Dalkeith Road, has urged the firm to stop the work.

He has warned that locals are unlikely to see or understand a vague paragraph, buried in small text on the seventh page of a pamphlet it issued prior to the work, about earthing electrical installation.

In it, Affinity says that many houses have used their iron water supply pipes as an electrical earth.

Although once common practice, this is considered dangerous and has not been allowed since 1966.

Affinity says: “As your new water main will be made of plastic, it is not suitable as an earth.

“If your electrical installation is currently connected to a metal water pipe for earthing, we strongly recommend that you contact an electrician.”

But Bernard warned that many houses in the area were built before 1966, and “might not have an alternative earth”.

He added: “The implications are serious, and Affinity shouldn’t expect people to understand that. It’s a failure of duty of care.”

Bernard said: “Most people will not have read the leaflet, and even if they had, few would be likely to understand it, and even fewer understand the serious consequences.”

And he warned: “Should an electric fault occur where no ground path is present, the potential is there for a person to touch some component of the system, and by accidentally providing a path to earth through their body, receive a burn or potentially fatal shock.”

He is particularly concerned that those who are frail or elderly will not understand the implications or even see Affinity’s text on earthing.

A spokesman for the firm said Affinity had a legal duty to inform customers when replacing older metal pipes with plastic ones as “they will not work as an earth”.

He added: “If customers are concerned their electrical system relies solely on a water pipe to provide an earth, they should contact an electrician to have it inspected.

“Affinity Water cannot accept responsibility for a customer’s electrical installation and our staff are not qualified to give advice on this.”