Abstract: A water well developer is connected between the end of a hollow drill string and an air-actuated well casing perforator to allow air under pressure to be transmitted through the developer to the perforator. After completion of the perforation, and without removing the perforating tool, a ball is dropped down the hollow drill string to block a passage through a piston that is slidably mounted in the developer, causing the piston to be driven downwardly and to unblock ports through which jets of air are driven into the interior of the casing. As the developer piston is driven down it also completes a relief passage connection that dumps air or water from the perforator.