Writing a blog post a couple of days later, Mr Gates argued that a direct downstream effect of open defecation by a majority of Indians is a "terrible diarrhoea epidemic" that contributes to 200,000 deaths every year because our water supply is contaminated as a result - other estimates put the number considerably higher. He quoted the World Bank report that estimated that inadequate sanitation costs India $54 billion (approximately Rs 3.2 lakh crore) a year, or six per cent of its gross domestic product (GDP). In an effort to proselytise for a cause that too few Indians speak about, Mr Gates optimistically headlined his blog: "The Next Great Market Opportunity: Sanitation for India's Poor." A precocious 15-year-old named Vitoria posted a comment below: "Thank God we have you on our planet!"
I share that sentiment - despite being a somewhat befuddled user of Windows 8 - and applaud Mr Gates' attempt to direct some of his wealth and marketing savvy at turning around India's lack of urgency on the subject of building toilets. Whether he succeeds is another question.
Although the government built 8.8 million and 4.6 million toilets across India in 2011-12 and 2012-13, there is a legacy of institutional inertia that led to this sorry situation where more than 600 million Indians defecate in the open. As both Mr Gates and a social entrepreneur interviewed on the foundation's website underline, the big losers from years of neglect on this issue are women and girls, whose health is affected disproportionately.
The good news is that the advances of science mean that building toilets for millions of people has never been more within our reach. Several of the options touted by inventors at the fair do not use water, which this country already suffers a scarcity of. (The average toilet in urban homes uses six to 20 litres every time we flush.) The cost of these unconventional toilets is dropping as well.
I spoke recently with Naveed Pasha of the Wockhardt Foundation about the biotoilets the foundation recently installed in Maharashtra. They consist of a prefabricated structure with an inbuilt WC and three slabs of cement and concrete. Inside the tank, which should survive 50 years, are bacteria. The principal discharge is water that is clean enough to irrigate fields. This product is relatively expensive at Rs 30,000, but - given its sensitivity to the environment and long life - worth the price. "Our motto is to stop open defecation," Mr Pasha says. This ought to be an anthem a genuinely patriotic politician could galvanise a country around. We could start with our corporate social responsibility programmes. The foundation started down this road to building toilets because the doctors in its mobile vans returned complaining that they were treating patients time and again for the same waterborne gastrointestinal diseases.
Walk around large Indian cities, let alone its villages, and public toilets are few and far between - other than in Mumbai. By contrast, in Beijing and Shanghai, I was struck by the fact that public toilets seemed to be on every street corner. In Bangladesh, open defecation has dropped over the past two decades or so to just 4.6 per cent, even if many of the toilets are crude pit latrines.
That poor sanitation is partly responsible for the wide prevalence of malnourishment in India is well known. Poor sanitation is estimated to be responsible for the fact that 62 million children in India under the age of five are stunted, or will not reach their full physical and mental potential. As a Save the Children study estimated in 2012, 43 per cent of children under five in India are underweight and about half are "stunted". That awful word inevitably correlates with subpar performance in school.
Our politicians have sporadically spoken about sanitation during this election campaign, but mostly in the manner of people who believe defecating should not be discussed at length in polite company.
The toilet fair in Delhi featured a US company that showed off a power plant that produced 150 kilowatts from human waste and a Beijing firm that used faeces to create a kind of charcoal. As so often in India, one feels the status quo can't continue but, despite all this creativity in the sector, it just might.
We may have put toilets within the reach of 275 million Indians in the past couple of decades, but that number is not nearly enough. As a pungent Associated Press report on the toilet fair put it, some 640 million people currently defecating in the open add up to 72,000 tonnes of excrement daily. It is enough to build 10 Eiffel Towers, a monument of national shame that undermines our claim to being a civilised country.
Twitter: @RahulJJacob