How to detect whether the groundwater in rural areas is drinkable?

First, I don't have testing equipment and technology. The easiest way to test the underground water in rural areas is to give it to horses. If horses like to drink, it's not a big problem. Donkeys and mules are not as agile as horses, but they are ok.

Second, it is best to use it to the local epidemic prevention station for testing. See whether the heavy metal content, Buddha content and other indicators exceed the standard.