White vinegar dissolves limescale. You can remove limescale from showerheads and taps by filling a bag with white vinegar and tying this around the shaft; remove and rinse them with hot water after a few hours.
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- How to Quickly Clean a Dirty Shower @ Good Housekeeping
Excerpt: If the water from your showerhead is shooting in all directions, or your low-flow has become a no-flow, the holes in your showerhead are probably clogged with minerals. Wipe the dry debris from the holes with the scrubber sponge you used for the tile. Still not spraying straight? Mix a solution of equal parts white vinegar and water (you’ll need about 1 cup), and pour it into a plastic bag. Put the plastic bag around the showerhead so the holes are immersed in the liquid, and secure the bag to the shaft with a twist tie. Allow it to soak at least 15 to 20 minutes (up to an hour if you can). Remove the bag and wipe away loosened deposits; run the shower on hot to flush the holes.
Image by Joydeep (Own work) [CC-BY-SA-3.0], via Wikimedia Commons
