PowerMaids

Try these techniques:

Depending on how bad they are a mixture of white vinegar and water (50:50) is an effective way to remove water spots.

If they are very bad then you should buy an acidic based cleaner to remove. Vinegar is mildly acidic so it will remove only so much. Go to your local janitorial supply store and buy acidic based bathroom cleaner and tell them what you are cleaning. You should have good success.

Be sure to wear gloves and follow safety instructions on the bottle for use and handling.

Be sure to start from the bottom of the doors as well to prevent streaks from forming from the acid wash.

If you live in an area where you have hard water then hang and use a small plastic squeegee in your shower and give your shower-door and quick wipe down at the end of each shower.

  How do I remove the ugly non-slip flowers and butterfly stickers from my old bathtub?

The adhesive used on these decorative non-slip pads are amazing. I have seen tubs with the surface of the baked enamel finish pulled up where the old sticker had been removed! In which case you need to repaint the area with touch up paint for bathtubs so it won’t rust.

Here are some ideas that have been successful:

Cover the sticker with tinfoil and heat with a hair dryer, once the sticker has softened, use your fingernail, cuticle stick, or plastic ice scraper to carefully lift up an edge being sure to get all the layers. Avoid metal edges, as you can easily damage the tub. Slowly pull up and peel back the strip, trying to keep the top layer and clear adhesive film layer together.

If the layers do separate and the film tears as you progress, lift other edges around the strips, working toward the center until all parts of the sticker are free.

WD-40 is effective at removing sticky residue from the sticker as well.  But the oily film from the wd-40 will need to be cleaned with soap and water once the sticker has been removed from the bathtub.