Water foundations can be vandalised
Running around a park may be good exercise for children, but campaigners say its effects are negated by a lack of drinking water.
The Children's Food Campaign (CFC) says few parks have water fountains, so children buy fizzy drinks to quench their thirst.
These often contain more calories than they have burned off, it says.
But officials said issues such as vandalism had to be considered when deciding where to put fountains.
Water fountains were a key feature of the public parks established to help people live healthier lives in the 19th Century because clean water was not widely available.
As that changed, fountains fell into disrepair or were removed altogether.
But, as the school holidays begin, the CFC says they are still needed.
It warns soft drinks are high in calories and that regular consumption has been linked to childhood obesity and tooth decay.
It has calculated that drinking a 500ml of Lucozade Energy Orange, which contains the equivalent of 14 teaspoons of sugar, would mean the average nine-year-old child would have to play football for one and a half hours to burn the calories it contains.
And it says a 500ml bottle of Fanta Fruit Twist, with around 13 teaspoons of sugar, would take them more than an hour of football to burn off.
It wants local authorities to provide adequate drinking water in all UK parks to ensure that children have access to free drinking water.
'Kids are kids'
The CFC said: "Children often have to go thirsty or visit ice cream vans, shops or takeaways where there may be few healthy options available and lots of tempting but unhealthy drinks and snacks on offer."
It said bottled water was not the answer as it was expensive and damaging to the environment.
Anecdotal evidence suggested the current provision of fountains in parks was "at least inadequate and often completely lacking", it said.
Jackie Schneider, who is co-ordinating the campaign, said: "As childhood obesity rises it's particularly important for children to get active, and their local park is a great place to do so.
"But when children end up buying unhealthy fizzy drinks because drinking water isn't available, all that exercise is wasted and kids could actually end up unhealthier."
The CFC is asking people to assess their local park's provision, and to contact their council if they are unhappy.
But a spokeswoman for the Local Government Association, which represents more than 350 councils in England and Wales, rejected the CFC's concerns.
She said: "To suggest children will always choose drinking water when it's offered is like suggesting they won't eat ice-cream if they are offered an apple.
"Kids are kids. The shops children are buying sugary drinks from will also sell bottled water, often at a lower price, and it is ludicrous to make out they have no choice but to drink something high in calories."
She added: "Water fountains are provided in many places, but decisions have to be made about how they will be maintained, whether they offer value for money, and whether they will be safe from vandalism.
"Parents aren't stupid. If they are worried about their children having enough to drink, being healthy and saving money they will take water with them when they go out, particularly during the summer."