“Water gets everywhere,” she explains. “It evaporates from rivers and oceans and rises up into the air. High in the atmosphere, where it’s cold, the water vapour turns to water droplets and begins to form clouds.

“They grow bigger and heavier, and eventually rain falls on the ground and flows into rivers and back to the oceans.”

“Let’s see what it’s like with our head in the clouds,” says Tom Pringle, better known as Dr Bunhead, as he holds a beaker from which thick white fog billows. His head is enveloped. He looks like a small cloud with ears, floating above a labcoat.

“This white stuff is water droplets,” comes Dr Bunhead’s muffled voice, “which is what clouds in the sky are made of. And because water has been cycling for millions of years, some of the rain that falls today has already been drunk by William Wallace,Julius Caesar and dinosaurs.

“You probably don’t want to know this, but every glass of water you drink contains particles of dinosaur pee.”

He comes down from the clouds to explain that the show is new this year, is in three sections - the water cycle, water treatment, and pollution - and is aimed at Understanding Earth and Space in the 5-14 guidelines (the water cycle; water as a gas; melting, freezing, evaporation and condensation; the existence of materials as solids, liquids and gases; waste water, treatment of drinking water, and pollution).

At the climax of the show a green plastic rocket, pressurised by a bicycle pump, shoots into the air, propelled by a jet of water. “These things can go hundreds of feet high,” says Dr Bunhead, “and when I first used them I was amazed how far they could drift in the wind. I can judge it better now, so I no longer have to ask complete strangers if I can climb their roof to get my rocket back.”

Douglas Blane. A teacher’s pack and video are provided with each performance of Wacky Waterworks, suitable for P4-7. To book, tel 0131 473 2070. Dr Bunhead’s website is at www.bunhead.com