I'm doing some research on aquifer recharge, and local government bodies are now finding it economically viable to capture and treat stormwater runoff, and pump into underground aquifers. A 'Water Banking' system has been in place in Arizona whereby water credits are given for every litre of clean water pumped underground into the aquifer, usually in the wet months, and debits in the dry months when the water is extracted. The aquifer acts like a bank's 'safe' to store fungible water volumes. It's an interesting system with some opportunity. Anyone heard any news on 'Water Credits' or the like in the pipeline? Any other water equities available?
You may call me a wimp, but when it comes to water, I see any form of gambling with a bad gut feeling. What "the markets" are already doing to food prices is critical enough, but ... I fear that the next major conflicts will be due to one country building some dam into a large river and cutting off the next country from fresh water supply. Seriously, what's next? "Air credits"? But if you don't mind that, it sounds like a great investment opportunity...
It will probably come at some point. The price of water keeps rising in no small part due to the fact that companies such as Coca Cola keep taking vast quntities of it for free. It's been a problem in India and other places for over 10 years now. http://en.wikipedia.org/wiki/Criticism_of_Coca-Cola#Water_use