I do generally agree that the price of water should go up, and that can be done in part by reducing the special subsidies currently given to agriculture (e.g. in California, farmers pay much less than anyone else, and generally less than the cost of even maintaining the state-owned aqueducts). But that's a different question from whether thoroughly securitizing water and trading it on futures exchanges would improve the situation. We could at least try the less radical change of "reduce the massive subsidies" first and see how large water users respond to a ramp-up in prices.