I don't want to help the water-cooling guy, but he is so clueless I can't help myself. You do know that all your water-cooled rigs are actually air cooled, right? I mean, the water goes through a radiator where a fan cools it off before being recirculated. The increase in room air temperature is the same whether your farm is cooled with air or water. If you spent more time thinking and less posting, you probably could have figured this out. Where did you think the generated heat went?
http://en.wikipedia.org/wiki/First_law_of_thermodynamicswhat if you store 2 metric tons of water in your back yard, and use the sheer volume of water to keep the temperatures down
Water is a huge sink, and 2 metric tons is not very much. You will still need active cooling on the reservoir.