While lurking the forum, I've recently read some things about water/magma that just don't seem right. Here are some observations I find very useful to know if you intend to work with fluids.
The bottom line is, distance is never a problem. Altitude is, tho... So, on to it.
1-Pressure.
Water (not magma) has the ability to move from a point to another point at lower altitude, provided there's a clear path. A clear path is only orthogonal movements (north, south, east, west, up and down, no diagonals).
Example, from my current fort, side view :
≈≈River≈≈≈██████████ █
█████████~██████████~~~█
█████████~██████████~~~█
█████████~~~~~~~~~~~~~~█
████████████████████████
Now this is useful! If you can lower your conduit, pressure will make water travel way faster, filling it all in no time! Afterward, water travels very fast to the end reservoir, regardless of distance (as long as it's all 7/7 water, easy if you don't have any surface).
2-Pump
A pump can move water and magma from a point to another point at lower or equal altitude, provided there's a clear path. Again, example :
███ █
÷÷~~█████~~~█
≈≈River≈≈≈███~█████~~~█
█████████████~~~~~~~~~█
███████████████████████
Pumps move water and magma very fast, regardless of distance. In fact, they are only limited by the amount of fluid they receive to pump. Not to forget it also moves the water up 1 level and keeps it there.
Why put 3 pumps side-by-side? Want 3 times the flow? Build them spaced out so their intake tiles get filled up faster, that's all you need.
Now imagine a situation with (1-) and (2-) combined, as follow.
≈≈River≈≈≈████████████████
█████████~████████████ █
█████████~████████████ █
█████████~█~÷÷~~██████~~~█
█████████~~~███~██████~~~█
███████████████~██████~~~█
███████████████~██████~~~█
███████████████~~~~~~~~~~█
██████████████████████████
The pump moves a gigantic amount of water in no time, since its intake tile is filled up by high pressure! Even with the right side entirely empty, it will fill up in an instant, probably emptying a part of the river for a little time. Want even faster filling of a bigger area? Replace the river with a 20x20x3 reservoir! At that point, your imagination is the limit. Of course, you need to power the pump, not use an operator, since the pump is flooded.
Note that the end water level is the same as the pump. With natural pressure coming from the river, it would go higher... If it was magma, with natural pressure it wouldn't even go up 1 level on the right side.
3-Diagonals
To prevent the effects of pressure and pump, you can use a diagonal. Water will seep through the diagonal and behave boringly on the other side. Say you designed a lovely waterfall in your statue garden, dining hall and booze stockpile, the 3 on top of each other. But too much water is going in the evacuation conduit! It clogs up, flooding both stockpile and dining hall! (totally not happened to me...)
The choice is yours.
Evacuate the water using (1-), a tall conduit. Pressure will move the water faster than a simple horizontal hall.
Evacuate the water using (2-), a pump. The horizontal hall is adequate, as long as the water has somewhere to go.
Slow down the flow before the waterfall, using diagonals. This requires arguably less work than the others.
Now, forget the designs using 3-pumps-wide conduits with 10 pumping stages back-to-back. Just plain inefficient! Sure, you want to move magma from one side of the map to the other. Use a pump! A single pump, that's it! Want more flow? Lower the pump, and build a mini-pump-stack at the recieving end if you really need the height. Or get magma from higher and use the drop to fill the intake faster.
There, I feel better now.
Edit : Anybody knows how to force dwarves to clean mud from their dining/meeting hall?