The bulb-pump handwashing station is sweet, but a buddy of mine has a setup that's a very functional, effective, and low tech alternative to the pump system y'all are talking about.
Take a small plastic tub (something like a 32 oz yoghurt container or large, sturdy cup) and put one or two small holes in the bottom on one side. Make the holes small enough so water will trickle from the tub no faster than about a pint or so per minute. Add a little hook at the top on the other side of the tub that'll allow you to hang it on the rim of a 5-gal bucket. Then get two plastic 5-gal buckets and cut away a deep, square slot in one of the buckets so it still holds a couple of gallons, and has about half or 2/3 of the original rim left (basin bucket). Use the uncut bucket as a reservoir for river water and add just enough bleach to the water to kill off germs. To wash your hands, simply scoop some of the water from the reservoir using the small tub, hang it on the rim on the inside of the basin bucket, then stick your hands through the slot and wash them under the water trickling from the tub. Pour what doesn't get used from the tub back into the reservoir bucket so you don't waste the disinfected washwater.
A picture would be worth a thousand words here but hopefully there's enough to get the idea. I like this system because there are no pumps, hoses, clamps, stainless steel tubing, etc.
Nothing in the world is more yielding and gentle than water. Yet it has no equal for conquering the resistant and tough. The flexible can overcome the unbending; the soft can overcome the hard. - Lao Tse