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 inst...

  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.