There are two basic types of cross-connections: a direct cross-connection and an indirect cross-connection. The difference between these two types of cross-connections is very simple. A direct cross-connection is subject to backpressure (as shown above); an indirect cross-connection is not subject to backpressure. An example of a direct cross-connection would be the make-up water line feeding a recirculating system. An over-the-rim inlet used to fill an open receiving vessel would be an example of an indirect cross-connection. Backpressure could not be introduced into the supply line with this type of connection.