Hi everyone, I'm new here (please don't think that makes my suggestion any less valid though).
Anyway, I've got a suggestion: Make Water Mills be able to accept water from Buildcraft liquid transport pipes.
Why? Because it makes no sense to send buckets of water through pipes in order to fill a "tank". It does make sense to send water through pipes to a mill/turbine however, that is how most water turbines work in real dams (drawing in water high up and letting it fall through pipes into a turbine). Even in the old days with wooden Water Mills people would dig shafts and channels to force water onto the wheel (because pipes weren't really an option back then).
Would that make Water Mills OP? I doubt it. Right now even the IC2 pump uses less energy to fill a bucket than a Water Mill can produce, yet no one considers it to be OP. Heck, even with the Thermal Expansion (which adds the Liquid Transposer that can fill buckets at low energy costs and insane speed) you're still better off with a field of Solar Panels. The setup to fill and transport the buckets (and the buckets themselves) costs so many resources you can build 2-3 times the number of Solar Panels. Especially in SSP, where you can skip nights with a bed, there is just no point in considering Water Mills if you compare them with Solar Panels if you ask me.
Also compared to something like a Geothermal Generator it would produce only a tiny amount of energy (1 EU/t vs 20 EU/t). You might argue water is infinite while lava isn't, but in the Nether it's pretty much opposite and combined with other mods you can produce lava from cobblestone, which again is infinite.
As for balance within IC2, it won't change anything. Geothermal Generators are a lot more powerful when combined with Buildcraft, I don't see why Water Mills wouldn't be allowed a similar advantage.
I'm not sure if this is something that needs to be changed in IC2 or if it should be adjusted in BC, but I think it's on IC2's side. If it is something in BC then disregard this, but please tell me so I can suggest it over there then.
Thanks for reading and I hope that you (Alblaka) will consider implementing this.