I don't have a huge number of birds now but the solution to keeping water clean for me and less refilling, was a couple of round plastic tubs with lids and a couple of gadgets i bought on eBay to push into the side. They screw in near teh bottom of the tubs and had small bowls attached so when the hens peck (they catch on quick) the water flows out to refill them.
When I had larger numbers my son bought a water butt with a lid and fitted drinker nipples to it - same principle except no bowls, so probably even cleaner