Michael Burry, of Big Short fame, is well known for moving his interest to water investment/trading many years ago
https://www.killik.com/the-edit/why-michael-burry-is-investi...
This article goes some way to explaining the rationale
Grain and cheese are the product of human activity. Fresh, clean water exists in plenty in nature.
Water shortages are local problems. The issue is just that a lot of the world's agriculture are on places with little water.
What do you mean by "nature"? Do you own the land where the water is, or do you simply plan on collecting rainwater? Otherwise, you don't own the water. This is a real-life problem that countries and communities the world over are dealing with.
Humans themselves need fairly small amounts for direct use like eating, drinking, hygiene.
Except in the places/times it isn't, which is much of the world for some of the time, and some of the world for much of the time.
Water rights exist, and who gets to exercise them in times of shortage can be very contentious, and even a cause for war.
Which is precisely why trading water futures is an immoral idea and can't be compared to trading any other commodity. There exist alternatives for every commodity on the planet (don't have oil? Use coal. No coal? Use wood, etc.), but there are none for water.
There's plenty of alternatives to any specific water, just use some other water. (And if you really want to, you can make water from oxygen and hydrocarbons.)
Not really no. It requires huge amounts of infrastructure, logistics, regulation to get it to people. Industrial activity, farming use water to make the food you eat
Difficult to extract, store and transport while maintaining quality.