Paph. moquettianum sp Isn't Growing

[Judi]

I started using rain water years ago before I got into orchids because I have well water that is very hard and left too much residue in the soil. Hardness is 240 mg/l; calcium is 88 mg/l; and magnesium is 20 mg/l. I flush all my chid under running tap water (unsoftened) once a month. Do you think it would be a good idea to alternate well water with rain water? And just out of curiousity, what is the physical benefit of calcium and magnesium? Is it necessary for all orchids or mostly for paphs?