Well first off, don't worry excessively about stagnant water - insects happily drink stuff that would kill us humans ...
Bees have been known to drink from puddles of cow urine, and similar sources.
But - if you want to provide a source of clean water, then here are a couple of ideas ...
The first has a photo, and needs no further explanation:
The second is the method I would choose, if my apiary wasn't adjacent to a dyke (local name for an irrigation channel).
It consists of a plastic container positioned on a stand - 5 gallons or so - and fitted with a tap near it's base. This tap is fitted with a 'drip regulator' such that a single drip of water leaves the container every second or so. If you measure the water level before, and after a set period of time, you can then figure out how often it will need re-filling (obviously).
Now comes the clever bit: running out from beneath the tap, and at a slight angle downwards (say, 5 degrees or so) is a long plank of wood. Set onto this plank are numerous angled battens, which cause this drop of water to zig-zag it's way along the plank, thus slowing it down, and wetting a much larger area.
I saw a photo of such a set-up 'somewhere' on the internet - the plank was covered in bees, and I've been trying to find that source again, without success. But I'll keep trying. I seem to remember it was located in Bulgaria or somewhere similar - halfway up a hill.
LJ