Good Magazine has a good graphic showing relative water use of daily activities. This is just a corner of it. Click to view the whole thing

Avoiding meat saves a LOT more water than a low flow shower head or toilet.

Growing corn requires a lot of water too:

A gallon of ethanol, depending on irrigation practices, might require up to 2,100 gallons of water to produce. While, in areas more suited to corn production, it can take as little as 100 gallons of water to produce a gallon of ethanol. The worst news of all of this, is that from 2005 to 2008 water use for ethanol production increased 246%, whereas U.S. bioethanol production has increased only 133%. This means that corn ethanol production has pushed into land that is not well-suited for growing corn, thus increasing water use far more than it increased yield.

– Ecogeek