Holy cow, folks. I can certainly see where an animal might get mired down in a tank (pond) and die but I have never heard of an animal dieing from drinking the water. My gosh folks, we've ran cattle for more than a sixty years on the same ranch and same tanks (ponds) and never lost one to anything that was attributed to the water, whether from drinking or wading. In fact, I swam in the ponds when growing up and never had any problems - but I didn't drink the water.
I think this may get back to taking care of your animals, vacinating, worming, etc. on a regular basis. My animals are healthy and they drink from stock ponds. And yes, I do provide clean, fresh water but the only time they drink it is when they are grazing in the area and when they haven't torn up the automatic valve.