I practice real estate law right near cottage country, where a lot of homes have septic systems, wells, or both. It is fairly common to have a separate septic and well inspection in addition to the general home inspection before the agreement goes firm, to make sure that any specific issues that relate to the septic system or well have been examined by a professional in the industry. The last thing you want after moving into your new home is to discover that there is a problem with the well, and that you have to cart in water until it can be fixed.
I was reading this article recently by Mark Weisleder, and I like the concept: maybe we should expand that rural concept of multiple inspectors to urban homes. Furnaces, fireplaces, mold: these are all areas of inspection that really do require specialists. A fire can be more devastating that a septic backup, and a general home inspector doesn’t necessarily have the expertise to determine whether the fireplace is up to code and in good shape. A furnace breakdown is equally inconvenient to well failure, and a general home inspector is often not permitted to pull the furnace apart to see how it’s working. It ultimately means more cost to either the buyer or seller, but it would be money well spent.