Scottish power, for example, offer 100% H2O derived energy for the same price as their standard tariff:
"ScottishPower pledges to match the electricity you use with the equivalent amount of electricity from hydro-stations .....
Green Energy H20 customers pay exactly the same for their gas and electricity as customers on ScottishPower's standard tariff."
Courtesy of Uswitch
If you aren't on a 'green' tariff already, would you consider changing? Particularly if it were to cost you no more than you already pay?
It could make a world of difference