Property: Doctor on the House - The curse of rising damp is just a load of old rot

There are building 'experts' who make money from persuading us that water is a bad thing. Ignore them, writes Jeff Howell

Viewed from outer space, the Earth is a very wet planet indeed: over 70 per cent of its surface is covered with water; huge masses of ice cover the poles, and there are billions of tonnes of water vapour floating around in the atmosphere.

Not that I've ever been to outer space, of course, but I've seen the pictures and, while Nasa might have removed the Stealth bombers on a recce over Kamchatka, I can't see them airbrushing out entire continents.

The blue wavy stuff is for real, and there's loads of it. So much, in fact, that under normal conditions everything on Earth, including building materials, contains a bit of water: bricks, timber, plaster, wallpaper. Even when they're dry, they're wet, if you see what I mean. We call this the hygroscopic or "air dry" moisture content, and it can range from around 2 per cent for old lime plaster up to 15 per cent for pine floorboards. This is a perfectly natural state for building materials to be in; if they were any drier they might crumble or crack.

The reason I mention all this is that there are companies with a vested interest in persuading the public that water is a bad thing, and that chemical methods are needed to keep it out of their homes. Of course, they don't refer to it as water because water has a nice, positive, thirst- quenching sound to it. Instead they call it damp, which sounds nasty and negative enough for you to want to get rid of it.

Now, the idea that water is bad and dryness is good is actually contrary to all biological sense; our bodies contain 65 per cent water, and we are far more comfortable in moist conditions than dry ones. Lost in a rain forest you could survive for months, but abandoned in the desert you'd be dead within hours.

So how has moisture in buildings become so demonised? It has happened quite recently; the term "rising damp" was not coined until the 1960s, when it was first used in the marketing literature of the damp-proofing companies. Before that, if a house was standing on such wet ground that water was being sucked up by the brickwork, draining the land was the usual remedy. It was only when silicone water repellents were developed that someone had the idea of squirting them into walls to form chemical damp-proof courses.

To exploit this idea commercially it was necessary to convince the public that "rising damp" was a widespread and dangerous problem. This has been achieved very effectively; it's become like the old joke about sanity: I'm sane, and I've got a certificate to prove it.

I have been quoted recently in the building press as saying I don't think rising damp exists at all. I think it is a myth, just like unicorns and fairies. The response from the damp-proofing industry has been swift and predictable; if rising damp doesn't exist, they fume, then why are there 2,000 companies in existence whose sole purpose is to eradicate it? And why do councils and mortgage lenders ask for guarantees that it has been treated?

Well, it's the emperor's new clothes, isn't it? You can't see the rising damp, and it has never given you any problems, but the specialist says he can detect it with his little meter, so you'll have to have it "treated".

This has given me a business idea. I'm going to spray people's homes with a delicately scented colourless liquid, and issue paper guarantees that no unicorns will appear for another 25 years. At a monkey a piece, I should soon be able to retire.