Turn off the water supply to the toilet
Flush to lower the water level
Pour white vinegar into the bowl
Let it sit for several hours or overnight
Sprinkle baking soda over the stained areas
Scrub with a toilet brush or pumice stone
Use a toilet cleaner made for hard water stains if needed
Repeat the process for stubborn stains
Turn the water supply back on
Flush to rinse the bowl
Wipe any remaining residue from the rim and bowl edges