1) Water is a life necessity, but it can also be a superfluous want (e.g. lawns) and it can also be a greedy natural resource grab (e.g. Nestle). Generally speaking, we have enough water to go around for human needs, but people regularly use the emotional appeal of human needs to justify low prices for their wants or exploitation. At the very least, financial markets for water are devoid of shallow emotional appeals to morality and acknowledge it for what it is. All that I ask is that we always ensure that human needs are met, and that is a job for governments. Let financial markets work with the rest...hell, the government should probably sell what's left over to the highest bidders.
2) the real difficulty of selling water is infrastructure. It's expensive, and unlike most commodities, it is almost completely fixed-cost. And the vast vast hypermajority of water consumers only have a single feasible source of water producers. The idea of water futures, then, seems a little absurd. This essentially limits trading to only those who can feasibly take delivery, and in reality that limits you to the same single-source provider you've had from the very beginning. I can't help but think that auctions or dynamic pricing are a better and more efficient idea.