A campaign for the drink Lucozade Sport has been banned following complaints about its central claim that the product "hydrates and fuels you better than water".
The TV advertisement and a poster drew 63 complaints, including one from the National Hydration Council, challenging whether the claim broke advertising rules.
The ad showed two groups of men, one drinking water and the other Lucozade Sport, running on treadmills while being monitored by technicians.
A voiceover included the line: "Lucozade Sport gives you the electrolytes and carbohydrates you need, hydrating you, fueling you better than water."
Pharmaceutical firm GlaxoSmithKline (GSK) said that the claims in the ad were based on the fact that Lucozade Sport is a carbohydrate-electrolyte solution.
The company said the claim that Lucozade Sport "hydrates you better than water" was fully consistent with the authorised claim "carbohydrate-electrolyte solutions enhance the absorption of water during physical exercise".
It said this claim was backed up by the European Union after a scientific assessment undertaken by the European Food Safety Authority.
The Advertising Standards Authority (ASA) said that GSK did not accurately reflect the authorised claim about carbohydrate-electrolyte solutions in the wording of the ad.
It ruled that it failed to make it clear that the benefits of the drink would only be achieved during prolonged endurance exercise.
It also took issue with the apparent claim that Lucozade Sport "fuels" you better than water.
GSK said it "strongly believed" that consumers would recognise that Lucozade Sport provided calorific energy, whereas water was calorie-free and could not provide "fuel" at all.
"Common sense dictated that the claim should be acceptable, because consumers were unlikely to misunderstand it," the company said.
The ASA said the ad must not appear again in its current form.
National Hydration Council general manager Kinvara Carey said she was pleased with the ruling, adding that water is "all that is needed" for the "majority of people participating in exercise and sporting activities".