We also have very hard water here as well. The best thing I have used is comet and a toothbrush. I sprinkle the comet on quite liberally and let it set for about 10 minutes, then scrub it off with a toothbrush.
Try putting some borax--stores sell in in the laundry detergent area--in the bowl and letting it sit overnight. If that doesn't work, try this as a next step:
Being in the house cleaning business for 25 years I have found a pumice stone works great. Just make sure the stone is wet.
I have used the pumice stone. "The Works" toilet bowl cleaner helps to.
this one is a little dangerous, but it will make the toilet look brand new. Pour about 2 cups of muriatic acid into the toilet bowl, place a newspaper underneath the seat, close, leave for about 30 minutes. DONE and won't have to be done again for quite a while, can also use in the tub.
@Antoinette Garton Would this be safe to use on a septic system when flushed and where do you buy it?
drop half of a Mr. Clean sponge in the bowl and let is sit overnight. it will be all clean in the morning!
Antoinette mentioned muriatic acid. Actually, any acid will work to some degree. My first attempt would be using Coke or any cheap carbonated beverage. I've used pumice too and it works, but you can damage the porcelain surface if you scrub too hard.
I have very hard water, I have been using a pumice stone for last 12 years so far no problems.
I also own a housekeeping company and for the weekly clean we use Borax as directed on the box, the longer it sits the better it works. For the tough hardwater ring and stains where the water runs down use the wet pumice stone. No harsh chemicals and all environmentally friendly. NOTE do keep the Borax away from pets and children.
@Patti Nicholas Great idea.
The pumice stone and borax as well as coke all work. Another option is to empty bowl of as much water a possible then saturate paper towel or cotton with white vinegar and place on the ring. Leave overnight or at least two hrs if on a schedule. Vinegar should soften lime scale enough to make it easily scrubbed away. If leaving in toilet overnight rewet before going to bed to keep action going.
I just tried soaking a cotton ball in hydrogen peroxide and gently rubbing with that. Presto! Worked great! I not only have hard water stains, but also a blue ring that was left from using one of the popular tank tablets.