During normal operation of a window air conditioner, water drips steadily from the condensation coils and collects in a pan on the bottom of the unit. A tube then directs it outside. For the water to flow in the direction it's supposed to, most units must be installed with the outside end slightly lower than the inside one. Check your unit with a torpedo level to ensure it's tilted in the proper direction. If it's level or tilted toward the inside, unplug it and readjust the braces. Or pull the base of the unit toward you and push its top slightly away, until your level indicates a tilt toward the outside. It's best to check for level along the flat bottom on the outside of the unit.
Note: Some units should be installed level because the tilt for drainage is built in. Confirm the proper installation with the owners manual or by looking up the model online.