Here's the setup in my current fort, Bodicetongues, but instead of water from a river, it's magma from a volcano. The principles are all the same, though.
Here's the pump house, the farthest building to the left, with walls to guide the magma. As you can see, I'm pumping it down a staircase, which makes building the thing a lot easier.
On top of the pump house is a windmill to power the pump. Because I'm cocky, I didn't bother putting in any stop mechanism; I just had them design the screw pump, then suspended the build job until I was ready to pump. I do not really recommend this unless you enjoy fun.
Yes, my depot is outside. I like it when they get ambushed.
Much farther down (and a little jog to the south, bypassing a tunnel I already dug): on the left is the magma coming down the staircase.
On the right is another pump, which was used to fill the big chamber to the right, which is right underneath my forges. It took the magma from one level down, which is...
...the reservoir. Of note are the four columns surrounding the up stair, which provide the diagonal flow that prevents the reservoir from overflowing. Should I have a need, I can tap into the reservoir from the level above at any point and it won't overflow. I'll probably never need to do that, but I like being prepared for possibilities.
The real point of this exercise is to show that the pump in the third picture is pushing the magma through the channel, rather than waiting for it to get there by itself. Much, much faster.
I should probably point this out: the tunnel to the lower pump (walled off in case of building destroyers) leads to the back of the pump, NOT THE FRONT. To pump, the dwarf stands on the back of the pump. Since there's no magma on her level on the left side, she doesn't get burned. If the impassible front of the pump isn't tightly sealed, liquid is gonna go everywhere...and you know what that means.
