What is the best way to clean hard water deposits from a shower head?

You can fill a small plastic bag half full with white vinegar and attach the bag over your showerhead with a rubber band. Leave the bag in place for an hour or two. Then remove the bag and scrub the showerhead with an old toothbrush or rag.

I have gotten the best results with CLR... fill a plastic zip lock bag with the CLR... put it over the shower head and tie in place... leave for at least an hour then rinse... repeat if needed

Soak the head in lime away toilet bowl cleaner. it cleaned off the BAAAAD water deposits from the water/ice tray on my refrigerator... just left it in the tray for like 10 minutes... it melted off.

Since your shower head is hand held... just soak it in a plastic (no glass in the shower!!) bowl

Lime Away or CLR. Just soak a bit and wipe clean!

Good for lots of stuff

vinegar and baking soda will do the trick