Let's wait to see which country, between China and India, can fare better over the next 60 years of economic development. India might not have enough water now but the raw material for solving any problem is found in problem solvers, not the ground.
That really depends on if India is able to successfully educate and/or provide useful skills training, health care, nutrition, and safety i.e. polish its "demographic diamonds". As well as maintain a healthy, competitive economy, rule of law, and respect for property rights - all of which creates an environment in which they can work hard and prosper.
There are countries with large young populations that struggle to make a decent living due to a lack of investment or opportunities.[1][2]
Since India already has nuclear technology, they can use it to desalinate large amounts of ocean water. Nuclear energy is relatively easy to scale.
Producing good doctors, teachers, police officers, judges is much harder to scale. At the very least, India us known to nurture good engineers and doctors in serious numbers.
India has more working-age people and is facing less of a population cliff than most countries. Whatever problems can be solved by workers, they will be in a better position to solve than anyone else. The US has immigration, India accomplishes the same thing but in one country instead of two continents.
China and India already had large populations compared to the western world, two centuries ago, and yet they were not doing better from an economic or military standpoint.
