Many home owners who use a well to get their water opt to have a water treatment system installed. The treatment system can help with many problems associated with drinking water - hardness, bacteria, odor, high levels of iron, etc. In some cases a backwash tube will be installed so the components can be flushed periodically and kept in good working order.
Pay special attention to the location where the backwash or drain discharges to - most towns do not want it to empty into the septic tank, and your septic contractor will advise against it. Salts and other minerals can flow from the treatment tanks inside your home into your septic system, causing premature erosion of the tank. Also, your septic system relies on bacteria to function correctly. Flushing salts and minerals from the treatment system into the septic system will hamper the bacteria from eating the solids in the septic tank, causing the system to function improperly.
In many cases it is impossible to see exactly where the water treatment discharge tube leads to - the tube will exit the house through a foundation wall and be buried underground at the exterior. Ask your septic contractor to check it out during a septic inspection. Also, check with the company who installed the treatment system for the location of the drain discharge. The installation company will usually leave a sticker with their name and phone number on the treament tanks or filters. If you are in doubt as to where the discharge leads to you can always have a new drain laid to an appropriate area (not the septic system) by your septic contractor or a well water treatment firm.