Concerns have been raised about the “shortage” of free drinking water available at Olympic Games venues.
Spectators are not permitted to bring more than 100ml of water into the Olympic Park and other Games venues but are told they can bring in empty bottles and fill them.
But today, the Commission for a Sustainable London 2012 has voiced concerns about a shortage of water at the sites.
The body, which monitors the sustainability of the Games, said there have been queues at all venues for water.
They accused London 2012 organisers of getting caught short and not anticipating the demand.
Shaun McCarthy, chairman of the Commission for a Sustainable London 2012, said: "London 2012 is the first Games in recent times to offer free drinking water, which is a huge moment not just for the Games but for the events sector.
"As such we are saddened to see that the organisers have been caught unaware and a number of venues have run out.
"We understand that Locog is addressing this issue and that they have a plan for an urgent resupply of drinking water and deployment of more fountains across venues. Let's hope they get these logistics sorted quickly."
Dr Emma Derbyshire, independent consultant to the Natural Hydration Council, urged fans to keep hydrated.
She said: "We are at the greatest risk of dehydration when we are too hot or too dry, have limited access to water, or need more water than usual - such as in warm or dry environments.
"Make sure you always have access to water, even when out and about, and consider bottled water when you are on the move.
"When it is hot and humid, it affects the body's hydration levels. To overcome that people should drink small amounts frequently.
"People attending the Olympic Park should seek out where they can fill up their water bottles.
"Access to water is important, otherwise symptoms of dehydration may kick in such as headaches, dizziness and poor concentration - which could affect people's enjoyment of the Games."