I had a couple cattle water experiences lately - I rotated my cattle into fresh pasture which included the "upstream" side of a conservation runoff collection dam which has refused to hold water except for maybe a 20 ft diameter stagnant puddle at the low point. This water is really rank much of the time. I usually have an electric wire around it but didn't when I first turned the cattle into this field. Nearby, no more than 50 yards from this stagnant pool is a waterer with some of the best well water on the planet sitting there for them to drink.
So where does 2/3 of the herd especially calves go as soon as they enter this new pasture??? Of course, right to the stagnant 20 ft diameter puddle, mostly covered with scum, and start drinking and urinating and defecating all at the same time into the same puddle! The waterer nearby with great well water was unused....
This just showed me they aren't very smart and rely on us to provide them with clean drinking water and also rely on us to keep them out of the bad stuff. I quickly put the electric wire up and then they went over to the waterer for their next drink.
Won't bore everyone with the second example but I agree with opinions above that good drinking water is very important to the health and growth and milk and therefore profitability of cattle.
The fact that they haven't yet died from drinking dugout water that they are also dropping manure into does not mean that it is ok, long term. As Dun points out, the numbers and density and flow of a stream may move or mask the problem but it is still potentially there and will likely cause a problem at some point. jmho. Jim