A pitless well adapter apparatus providing an easily assembled coupling through a well casing between a well drop pipe and a water delivery pipe. The coupling members include an adapter body member connected to the drop pipe, and an adapter outlet member connected to the delivery pipe and firmly mounted to the well casing through an opening therein. A U-shaped skirt is formed around a side opening in the adapter body and has a beveled groove formed around the inner periphery thereof. A U-shaped beveled flange is formed on the intake end of the adapter outlet member and is shaped and sized to closely mate with the groove in the skirt on the adapter body. The adapter apparatus is assembled by lowering the adapter body, with the drop pipe connected thereto, until the grooved skirt of the adapter body member is fully engaged on the beveled flange of the adapter outlet member, at which point the interior bores of the adapter body and the adapter outlet member are in full communication to allow the flow of water therethrough. The engaged beveled flange and grooved skirt extend below the lower margins of the interior bores of the engaged members to substantially prevent relative parting movement of the two coupling members due to pressure moments.