Well, I don't know about the problems with well water. Guess its hard with minerals?
Anyway, depends what you want to do and also how new the sail actually is. If its an older one that is no longer in its "racing" prime and you are just looking to reduce the stains and clean, then read on. If relatively new, then get others' viewpoints.
Attached is a pic of my spring laundry "close-line". The sail is a 135 genoa with a 43' luff. Not much different in size than yours.
Stetch out some old halyard line as in my picture. Depending on how high you can tie and how tight you can tension the line, you might need to support in the middle with a 2x4 or two. Drape the sail over it in calm wind conditions.
Make a solution of your cleaning solution. (I won't go into that because there are many opinions here about what is best and you'll get warnings about ruining the sail.) Put the cleaner in a garden sprayer. Early in the morning when temps are cool, low/no sun and humidity high, spray liberally onto the sail. Or you can slop on the cleaner from a bucket and a floppy brush. Let soak/penetrate for a while as you sip some early morning coffee. Then blast away with a garden hose working down from high to low. Also a pressure washer is great if you use the wide spray pattern and don't get too close with the nozzle. Get into the "tunnel" under the close-line to do the same with the hose or the pressure washer on the other side (inside) of the sail. Expect to get wet doing this.
The sail should end up much cleaner. To remove rust stains, I use an oxalic acid based cleaner followed by a rinse. Several applications might be necessary, but eventually the rust will go away, or at least be a lot less noticeable. After removing the rust, see if you can observe what is causing the stains on the sails and rectify. For instance, on my boat, the ends of the 3/8" bolts securing the boom bails through the boom were prone to rusting a bit and transferring onto the flaked mainsail. I have painted the ends of the bolts with clear automotive lacquer and the rust stains on the sail now longer happens. (Tip: You can do the oxalic acid thing this while sailing if the weather is calm. Just brush over the stain with a brush. A couple of times later, there will be no stain left when you douse the sail.