I think you should shorten your investment horizon. A week is way too long.
Long-term, I LOVE some of the water ETF's...it's the next oil.
Perhaps VERY long-term. I don't like them, personally. If you're looking to invest, be careful of some specific factors;
Agree with desalination. There are ways to invest in actual water though .. Though far more rare than the REIT-like real estate deal, that also include water.
TBT is always fun to track and has made a good move upward recently, after falling forever. I've never been good at the Ben Bernanke is speaking on Thursday so take a position now and hope he says whatever you want style of trading though.
Some farmers can get government subsidized crop insurance, so I wonder how much incentive they have to invest in this technology.