> as you may have metioned

Ya that's basically what I had in mind.

A number of watermills use a wooden trough construction which either lifts the water high enough by using a lesser slope then the rivers surrounding geography or directs water from a uphill resivuare like a dam. (see pictures at the below) So in clonk the source would create a small body of water on top of a cliff which would flow over(or out of) the cliff and into a pool below(which would slowly leak out so the level doesn't get flooded). The other posibility would be to just have the source in midair dropping water into a pool and the watermill could be built between the source and the pool.

Sorry this post turned out longer then I meant to make it >.<

Fairly good side view: http://www.fiddlersgreen.net/buildings/watermill/IMAGES/mill-photo.jpg

From wikipedia: http://upload.wikimedia.org/wikipedia/commons/8/8c/Kyoto_Botanical_Garden_-_water_mill.JPG%5b/img%5d

BTW I would have put the images into the post but they would have been huge according to the preview O.o

Edit:

> waterfalls may be very static and have to be placed by a mapdesigner

That is a good point. Automated water source placement would need a good procedural generation script.

> Show some solidarity to renewable energies!

Hehe. But we already have windmills. (which work way to well and consistently btw :P)