Compact watermills (UNMANNED ONLY) would work, given enough calculations.
Pumping water into watermills makes even less sense than the unmanned mode.
For example :
1 watermill calculates a 3x3x3 (25 blocks max due watermill and cable) outputting up to 0,25 EU/t
"LV" (8 ) watermill would calculate a 7x5x7 (242 blocks max due watermill and cable) outputting up to 2,42 EU/t
"MV" (64) watermill would calculate a 13x11x13 (1853 blocks max due watermill and cable) outputting up to 18,53 EU/t
"HV" (512) watermill would calculate a 25x23x25 (14363 blocks max due watermill and cable) outputting up to 143,63 EU/t
"EV" (4096) watermill would calculate a 49x47x49 (112823 blocks max due watermill and cable) outputting up to 1128,23 EU/t
Fancy rotors could be added.
I know this is not realistic, but at least follows IC² "unmanned" aspect.
Real watermills would require a big dam + waterfalls + watermills with rotors on the end of waterfall to transform gravitational energy into kinetic and then into electrical.