I often have a scummy stagnant small pond/puddle 50 yards from a waterer with some of the best well water in the world.

With both available to the cows and calves it seems like most of them would prefer to be standing in the scum, dropping manure out one end into the water and the other end drinking the same water. So I do not have much confidence in cattle's ability to make good choices of water.

Since seeing this I always put an electric wire around the "puddle".  Many cattle disease problems can be passed with bad water.

I would suggest you put a hot wire around the pond and they will drink from the stock tank.  jmho.

Jim at Dawn