After offering new age IT solutions to the world, Microsoft founder Bill Gates has now set his eyes on achieving his 'ultimate' dream - low cost toilets.

Come August and he will host the world's best scientists and engineers in Seattle, US, to see if they can design cheap, dry toilets which don't hitherto exist.

This public health innovation, says the co-chair of Bill and Melinda Gates Foundation, is his "ultimate dream" though it is "not the only one".

"The ultimate dream is this so-called dream - that of a toilet design," Gates told a select group of journalists here today, but added that it was not "the only dream".

Gates said, "There's expertise all over the world in this. We're putting money and asking people to come up with a cheap design. And, actually this August we have scientists, engineers from all over the world come and tell us (on this)."

He said his Foundation has thrown up this challenge for quite some time now and hopes to get his "dream toilet" soon.

"It should be possible to have a toilet that does not require running water, whose cost is very low and whose smell characteristics are as good or better than a flush toilet. But, it doesn't exist yet," he said.

He added, "Let's see what they come up with. If they don't come up with anything then we will put the challenge out again. Maybe get a new group of scientists to work on it."

Gates is in India to review the projects being run by his Foundation.

Low cost dry toilets, if created, would prove a boon to public health in the developing countries where lack of hygiene is a principal driver of disease and malnutrition.

In India alone, only 46.9 per cent of the total 246.6 million households have toilets at home. Of the rest, 3.2 per cent use public toilets. If that was less, 49.8 per cent use open spaces for defecation.

The Rural Development Ministry under Jairan Ramesh is also launching a campaign to make India open defecation free.

Gates, one of the world's greatest IT innovators, is hopeful that some solution would come up soon to this public health issue.

He said flush toilet is considered the best in terms of smell and appearance the world over.

"The world's got a problem in that. The best toilet is a flush toilet in terms of just smell, appearance...anything else is vastly inferior and yet the cost to doing it that way. It's a very inefficient...So it's kind of unfortunate that there's not something where you look at it and say that's just good," he said.

Gates, however, said that besides finding a solution to the world's hygiene problem, his Foundation is doing a lot in sanitation.

"That's not the only thing we do in sanitation. We are also involved in total sanitation. We're done a lot of field based, more practical problems. We are doing things like trucks that clean up latrines more efficiently," he said.

Gates, who has now taken up to philanthropic activity across the world, says finding a solution to the hygiene issue by inventing the toilet is not his 'only' dream.

"It's not a ultimate dream. It's not the only one. It's a Polio-free world, HIV-free world, Malaria-free world..." that he dreams of, he said.

Census figures release in March this year also show that only 32 per cent of Indian households use treated water for drinking and 17 per cent still travel more than 500 metrs in rural and more than 100 metres in urban areas to get water.

Gates' solution of cheap toilets that don't require running water but can still deal with the issue of stench can work wonders for India, where approximately 400,000 to 500,000 children below five years of age die due to diarrhoea annually. Improper disposal of human excreta is a major risk factor fo diarrhoeal diseases.

But Bill Gates, who plans a major investment in India over the next four years, believes the sanitation problem can be solved.

If that happens, India's progress towards most Millennium targets would speed up and the problem of scavenging would also be addressed.