The unsightly build-up is mineral deposits. To remove these deposits from the showerhead, take a plastic bag and pour a cup of vinegar in it. Place the bag over the showerhead and use a twist tie to hold it in place overnight. In the morning, remove the bag and use an old toothbrush to gently scrub off the deposits. You might be able to remove the aerators from the faucets and allow them to soak in the vinegar overnight.