Indian or foreigner, you will not be surprised to hear that one of the first and most shocking things I learnt when I moved to India recently involved toilets - or rather the lack of them. Jairam Ramesh, who was at the time the minister responsible for sanitation, explained that between 400,000 and 500,000 Indian children under five die each year from diarrhoea, the largely preventable result of poor hygiene.

There are two shocking things about this number: its magnitude and the gap between the upper and lower estimates. The range means either that up to 100,000 children are dying in addition to the known 400,000, or that they are still alive. Or perhaps the extra 100,000 do die annually, but not from diarrhoea, for the total number of under-five deaths is a still more chilling 1.66 million - roughly equivalent to the population of Qatar or Hawaii.

My purpose is not to criticise India or Ramesh - who has campaigned vigorously to end the health scandal of leaving 600 million Indians to defecate in the open - but to point out the terrifying scale of the challenges facing a country that will soon overtake China to become the world's most populous nation.