The Local Government Association, which represents more than 370 councils with responsibility for public health, says tap water needs to be made more freely available, rather than something you have to ask for.

It wants the Government to use its forthcoming childhood obesity strategy as an opportunity to encourage restauranteurs to take responsibility and offer parents and children the choice of tap water as an alternative drink.

Cllr Izzi Seccombe, LGA community wellbeing spokesperson, said: "We want restaurant owners to play their part in tackling childhood obesity by offering families tap water.

"While most restaurants will happily provide a glass of tap water on request, we're saying it shouldn't be something you have to ask for. Some people may be too embarrassed or find it awkward to ask for tap water. Others may simply forget it's an option.

"Water brings important health benefits and keeps people hydrated. For children it's an alternative to a sugary drink, while for adults it might dissuade them from ordering another alcoholic drink."

One-in-five people do not know that licenced premises have to provide free tap water by law. Many restaurants however, currently only do so on request.

Eight out of 10 people usually drink tap water at home, yet only a third do so when eating out at restaurants.

The same survey also found that 15 per cent of people who usually drink tap water at home, never think of asking for water in cafes or restaurants, while 13 per cent said it made them feel awkward.