@jason morgan,
I can and has been done with hard water for many, and many have been unable to. At times I do switch to RO and then back to tap every other res. change. IMHO, I don't think it is really the high PPM from the tap but what is actually dissolved in the tap water. That will differ from town to town and well to well.
I have heard of people using those cheap camper water filters that go inline with a garden hose to reduce the PPM. They are not RO filters but will catch some of the crap. I use two together to fill my hot tub because unfiltered water will leave a white powder on the bottom after 24-48 hours. We don't drink the tap water either because it is just under the FDA's PPM limit for safe water. I use my RO machine to re-fill my water cooler jugs for drinking water.
Many say not to use water that has went through a water softener due to the amount of salt that gets in it.
I will say between RO and tap water, tap takes a hell of a lot more PH down than RO does to adjust and maintain.