Calcium, lime, magnesium and iron, naturally found in hard water, attach to just about every. Green or brown stains in the toilet usually indicate lime buildup.
Step 1: Use the plunger to clear all the water out of the toilet. Step 2: Pour the cleaning vinegar into the bowl until it covers up the hard water stains. Step 3: Soak toilet paper in the vinegar and apply it under the rim of the toilet, making sure it sticks to the bowl.