Hashing with the cash at 30C has given me a huge increase in MH/J
How much do you think is the gain in MH/J with water cooling?
https://bitcointalksearch.org/topic/3x7970-mining-results-57410
He was using 232W/card at stock clocks on air, while using 191W/card at stock clocks on water. So about a saving of 40W, or if you rathar deal with MH/J numbers it's 2.37 MH/J (air) to 2.87 MH/J (water).
If you pay 10c/kwh, the waterblocks save you about $35/year.
I still don't see how swapping out 1 fan for a watercooler saves 40W...
Watercooling allows the GPU to run much cooler.
If temperatures are high, resistance is also high. It requires more power to overcome that resistance.
This therefore saves a good amount of energy.