Abstract: An air gap drain module for use with the dispensing head of a reverse osmosis dispensing system for potable water has an inner waste water tube and an outer drain tube which are disposed concentric to each other at one end and for a portion of the length of the inner tube adjacent the concentric end. An air gap in the form of spaced slots is provided adjacent the concentric end of the drain tube and a closure is connected to the common end of the waste water tube and drain tube with an annular flange or skirt thereon in assembled position disposed to extend between the waste water tube and the drain tube to form an annular passage about the waste water tube and direct the movement of process water issuing from the concentric end of the waste water tube into the drain tube. The closure forms a chamber or trap with the adjacent end of the waste water tube which in conjunction with the spaced slots prevent back flow into the waste water tube.