Remove water chamber (reservoir) and unscrew the nut from the mounting plate. Position the mounting plate and holder on the outside of the cage with the trough protruding through the bars. Push the screw from inside the cage through the bars and through the hole in the mounting plate. From the outside of the cage, screw the nut onto the screw post. Do not over tighten. Fill the water chamber. It is not necessary to remove the cap with no-spill valve. Turn the water chamber over. The no-spill valve will close and prevent water from flowing out. Set the water chamber into the holder. The no-spill valve will open and fill the trough with water. Important: To remove holder without having to unscrew the nut: For Horizontal Bars- Remove water chamber first, then squeeze holder and pull straight out. For Vertical Bars- Lift holder and pull out.