I've used the Prestone flush kit for many years on many cars - it works well. When you drain old coolant, catch as much as possible and dispose of it correctly. Glycol does biodegrade in nature, but slowly, and meantime it's poisonous to small animals (or your kids if they think it's Kool Aid). Should be no problem flushing the system with garden hose water, even if it's "hard" (lotsa minerals). It's only in there a short time and doesn't heat up to the boiling point, so there should be no (or extremely minimal) deposits. After the final flush, drain, fill up with distilled, run the engine a minute (the heater is on FULL HOT all the time you are doing any flushing/rinsing), and then drain again. Fill one-half the specified capacity of your system with your preferred 100% anti-freeze and top up with distilled water.

After running the engine for about 10 minutes to get things up to full temp and check for leaks, I drain about 1qt into a container from the block drain tap, then pour this back into the coolant reservoir. This way all the coolant is thoroughly mixed in all parts of the system.
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Bob (81-244GL B21F, 83-244DL B23F, 94-940Sedan B230FD)