"Modi has India talking about toilets. This is not the kind of issue that most politicians like to talk about. But I would guess that in the short time he has been in office, Prime Minister Modi has done more to raise the awareness of the need for toilets than any other leader since the country gained independence," Gates said in a blog post titled 'Meeting the New Prime Minister.'
In the blog, Gates writes about his meeting with Modi in New Delhi last month when he and his wife Melinda focussed on toilets, vaccines, bank accounts and health clinics in their "more than an hour" long discussions.
"We came away impressed by his commitment to fighting poverty and improving health for India’s poorest people," Gates said.
"This is an exciting time, not just for India, but for everyone who cares about giving the poorest people a chance to lead healthy, productive lives. With all the attention and innovation going on in these areas from health to financial services we have a fantastic opportunity to make an impact.
It’s inspiring to see India moving to the forefront of these efforts," he said.
Gates said Modi "made it clear" that he is "frustrated" with the slow pace of improvement in expanding and improving sanitation services across the country.
Modi, who wants to end open defecation by 2019, shared with the billionaire couple few of his ideas, including installing toilets in bus and rail stations in 500 towns.
Gates said Modi has been "quite outspoken" on open defecation, a subject one hears much less about.
"It may seem surprising when you think about all the innovation coming out of India, but 630 million people there defecate in the open because they don’t have access to a commode. Worldwide, the number is 2.5 billion people," he said, adding that creating good sanitation options for people is a big focus of the Bill and Melinda Gates foundation.
Gates discussed with the Indian leader the opportunity to design 21st century toilets that do not need big sewage systems and water treatment plants.
He praised Modi for being "generous" with his time with them even though his office was busy with the visit of Chinese President Xi Jingping and the floods in Jammu and Kashmir.
"Judging from our time there, it sounds like he's setting aggressive goals and pushing people to get them done quickly. He's having a lot of intense meetings with various ministers, asking them, 'What can you do in 100 days? Can you make your goals more concrete? More ambitious?'," Gates wrote.