When your useful water reaches the stable, the animal herd will add bacteria to the drinking water when they drink from a common drinking place or
by, for example, intestinal bacteria ending up in the drinking water. Then it does not matter that you have a good incoming water, municipal or from your own well. If you do not disinfect the water, there will be a steady growth of unwanted bacteria in the drinking water no matter how much you clean.
The reason is that the bacteria settle where you can not clean. In pipes, nipples, behind plates, valves etc. They can move upstream in a pipe with a pressure of 10 bar. They form a biofilm that is simply a factory for bacteria. It will continue to produce more bacteria until you remove the film. And you can not do that without using a continuous and effective disinfection.
and the stable environment expose the animals to a high bacterial pressure. In that situation, not much is needed for the bacteria to affect the animals’ appetite, growth or create infections and diseases.