The Local Government Association, which represents more than 370 councils with responsibility for public health, is calling for water to be made more freely available in schools, nurseries and children's centres to help make youngsters drink it more.
It also wants the Government to make hydration in schools a part of its forthcoming child obesity strategy.
Izzi Seccombe, LGA community wellbeing spokesperson, said: "Children and teenagers are not drinking enough water. It is far too easy for them to choose a soft drink rather than a glass of water. We need to reverse this and make water more freely available in our schools, nurseries, children's centres and colleges.
"The healthy option should be the default option. We want to make it just as easy for children to choose water as it is to choose a soft drink that is piled high in sugar.
"Swapping sugary drinks for water could make a big difference in helping to tackle major health problems such as obesity, diabetes and tooth decay, as well as improve concentration in the classroom."
Children and teenagers get less than a quarter of their recommended daily fluid intake – approximately eight glasses – from water.
Council leaders say tap water needs to be "the default option" for young people, rather than squash or fizzy pop that is high in sugar.
Fluid intake is at its lowest in the morning, at a critical time when children need water to help them concentrate at school. A recent survey found just 6.1 per cent drank water in the morning, compared with 24.4 per cent at lunchtime or 33.5 per cent in the afternoon.