Most people reach for bleach to obliterate toilet germs and stains but what about Vinegar?
Green living expert Mark Lallanilla says that plain old white vinegar is not only an effective cleaner, but also safer than chlorine bleach.
To eliminate hard water stains, soak toilet paper in vinegar and place directly on top of the stain. Let the vinegar-soaked paper sit overnight. The next morning, flush to rinse and the stains should be gone.
Source of information: About.com