They've been all the rage at this year's festivals, but just how practical are they? We look at how they work, what they entail and just how different they are to a 19th century outhouse.

"Better than sex!" was how one happy user reacted.

"Wish I had one in my house!" said another.

They were referring to that most precious of necessities most of us hardly ever like to discuss, let alone gloat about.

The toilet.

But this wasn't just any old loo - it was a compostable one. The kind where your excretions aren't swept away by litres of water, but mixed with vegetable peelings, shredded paper and old woodchips instead.

If it reminds you of camping, or Aunt Edna's old outhouse that no-one's used since 1843, then think again. These days, compostable toilets are better aerated and more eco-friendly than most loos we use now.

And some are calling them the toilets of the future.

:: How do they work?

Anyone who's been to a music festival in the past two years will have seen the composting toilet tent Comfy Crappers (www.comfycrappers.com) - or at least the people standing outside it.

Customers tend to queue for long periods of time for the alternative to smelly porta-loos, and are charged separately for numbers one and two (frequent users buy weekend-long wristbands for £13.50).

The sit-down loos compost poo amongst piles of hay and sawdust and - amazingly - they don't stink. The feedback has been startling. Comfy Crappers' users frequently cite the "absolutely brilliant idea" and "superb service" provided - as mirrors, wash basins and bingo are all also included in the experience.

Unlike conventional toilets, the composting versions rely on the power of nature to decompose itself, without the aid of chemicals or U-bends. They use little or no water, are independent of sewage systems and produce a valuable gardening by-product: compost.

Composting loos treat "humanure" by working on either a batch or continual process system. Batch systems have containers that are filled then composted, during which time a new container is used. Continual process systems, on the other hand, are both used and composted at the same time.

And, as eco-loos vary in their size, style and function, they can range from owner-built, two-chamber systems, to full-flush systems that operate on a centrifugal action to deposit waste into a composting chamber.

:: Compostable?

It sounds messy but, like all organic matter, poo decomposes naturally and becomes a nutrient-rich material that can be buried or used on flower beds and vegetable patches.

But if you're worried that your loo would yield an untenable thousand litres of compost per year, rest assured, says Scott Smith of Envirolet, an international company specialising in green loos.

"The amount a composting toilet actually produces is not as much as you may think per system," says the Canada-based marketing director.

"Human waste is almost 85-90% liquid, so the actual volume of what enters versus what exits is significantly reduced."

While Envirolet has been around for the past 30 years, the modern-day compostable toilet is said to have been created in Scandinavia in the 1960s. It then became popular particularly in Canada and Australia - where costly sewage systems have forced homeowners to think more greenly.

But the eco-loo has long been a contender to the WC even in the UK, as an advert for the Self-Acting Earth Closet, published in the April 1881 edition of The Ironmongers' Catalogue (and reprinted in eco-loo blog compostingtoilet.org) shows.

The "substitute for the Water Closet, securing healthy homes, inoffensive drains, and garden fertility", was said to avoid pollution of rivers and watercourses - and was a real steal at 55 shillings!

:: Why would i want to do this?

Primarily for the environment. Sewage systems can leak effluents into watercourses and oceans, disrupting and even killing marine life. Raw sewage can contaminate both water and food supplies.

And, most importantly, the water that we treat and then use to flush away our waste is becoming a resource that we should focus on saving, says Smith.

"More than ever, water is a valuable resource that needs to be saved for drinking - not used for flushing," he explains.

"This is especially true in developing areas. In developed areas, saving water is just as important, as is using alternatives to septic tank systems, which are just not eco-friendly."

Compostable loos are also cheap to run. Because they're independent of any sewage system, they could reduce your water usage by 20-50%, according to compostingtoilet.org A final benefit is that the the composting toilet doubles as a compost bin. Food scraps, garden clippings, paper, cardboard and kitchen grease and greywater can all be composted along with the human waste, thereby further reducing your overall waste.

:: Is it a viable alternative?

If you live in a high-rise, probably not - but that's only due to the height, space and venting requirements required for an eco-loo, says Smith.

"We've sold composting toilets to almost any imaginable type of application," he explains, "including homes, cottages, pool cabanas, warehouses, airport hangars, guard towers, treehouses, sky cranes and bridge towers.

"We sell a lot to narrowboats, cottages and churches in the UK, and interest is continually growing. The only application that we say, so far, is not possible is an airplane. But we're working on that!"

Unlike conventional loos, which require water, pipes and overpriced plumbers to be installed, a compostable toilet is generally pretty simple to get going yourself. You could even make your own green loo if you really wanted to (check the Centre for Alternative Technology's free information service, www.cat.org.uk, if you're interested).

But if you wanted to buy one, you could have yours up and running in a few hours, although Smith concedes that the venting is the most difficult part.

:: Doesn't it smell?

That's where the venting comes in. But as long as your loo is correctly installed and operating, you shouldn't smell a thing.

Most home-made loos tend to use woodchip to help the composting process, with some houses requiring separate urine and poo buckets to diminish smells.

Manufactured loos, on the other hand, like Envirolet's, can operate on fans and wind turbine ventilators to help with the aeration process.

But whether you make your own or buy one, compostable toilets usually smell less than their conventional counterparts, as the by-products of sewage treatment and septic tanks are nutrient-rich effluent, flammable methane and other stinky gases which give toilet waste its noxious odour.

:: What about cost?

An eco-loo could set you back a hundred pounds or a few thousand, all depending on your comfort level (do you want a bucket or a real toilet to sit on?) and hands-on attitude to making your own.

Be aware that manufactured loos increase in price the larger the "load" they're due to carry and the system they use. But that doesn't mean that you shouldn't try one yourself.

It might not be "the best poo of your life", as one Comfy Crapper user enthused, but it could certainly be the most ecological.