If your farm is located near a military base or industrial complex, and you obtain your water from a well, there is a contaminant you need to be aware of: perfluorooctane sulfonate or PFOS. This substance is not found in nature, but it is produced when many different products, from firefighting foams to plastic coatings, are made and used. There is a good chance it is found in your well water, and so it's essential that you choose a well water filter that is specifically designed to filter out PFOS.