To de-clog them, soak the showerhead in vinegar. If you can't remove the showerhead from the arm, you can still absorb it by using a plastic bag and a rubber band. Fill a plastic bag with vinegar and wrap it around the showerhead so that the holes are completely soaked. Hold the bag in place by looping the rubber band around the arm, and leave it for one or two hours. Remove the plastic bag and rubber band, and turn on the shower to flush the loosened debris. This same idea applies too battling mineral deposits on your faucet.