How do you get calcium stains off bath basins and toilets?

Try Bar Keepers Friend for scouring.

For really stubborn deposits wet a cloth with straight white vinegar and place over the top overnight.

If that doesn't work, then a pumice stick (my dollar store sells them) will certainly remove the deposits.

A product called the Works sold in most Dollar Stores. I had issues with calcium buildup and wasted TONS of money on all of the standard stuff people said to use to no avail. I even drained the bowl and tried to get if off using the back end of an old toothbrush. Nope. ONE treatment of "The Works" toilet cleaner overnight. GONE 100%. Then I did the tank the next day. Unbelievably clean. Best part is it's only $1.00.

Hello

I would suggest a CLR or LimeAway cleaner for basins showers or tubs.

For toilets

My solution was the pumice stick.

This is excellent way to remove stains and rings in the toilet. Great for thick crusted calcium mineral build up that the toilet waterbowl collects.

When commercial toilet cleaners fail -this is my go to. Koolaid did not work for ne.

They are found at my local Walmart for less than two dollars -good for multiple uses. Be sure to follow the use instructions, soaking the pumice stone in water for a few minutes. While the stone is soaking, grab your toilet brush and splash water up around the ring. Note: It’s very important to keep both the stone and the surface wet while cleaning to avoid scratching your porcelain toilet.

Additional information can be found here.

https://bradburybrothers.com/blog/plumbing/plumbing-emergencies/top-5-tips-help-hard-water-toilet-tank/

I have really hard water at my home. The simplest way I have found to fight the dreaded ring is to put 1/2 bottle of vinegar in the tank on the toilet - let it sit for about an hour - or longer - and then flush. I do this once a month to keep it in check. I still do the regular cleaning with toilet bowl cleaner as well.