Algae in the cow water

I have always been told that all animals (whether dogs, cows, cats, horses, or any other) should have clean water available all the time. I have always been told that clean means no algae! However I have been told by local folks here in India that they think cows should have algae and will actually add algae to the animals' water if it isn't growing. Has anyone here had experience with this?

Algae grows on all my stock tanks, buckets, etc... and when the water level is down enough the horse, goats, cows will eat it off the sides. When i do clean a tank out the chickens peck thru the pile of green stuff. I live in a warm sub tropical climate and keeping water free of algae is a severe waste of time an resources in my opinion. I keep fish in the stock tanks and they eat algae off the sides also. I'm sure there are many types of algae and some not so desirable... But it even grows on the sides of our well pipes. So, I'm sure my in house water has been in contact with algae....