The water isn't a concern... 180 ppm isn't particularly hard, southern California water is a lot harder.
I agree, L. anceps should be able to tolerate all of the conditions. Most Catts should be fine, protected from direct sun. In case of that rare snow, I'd suggest just covering the plants with a tarp. A string of those "old fashioned" incandescent Christmas tree lights can also give a bit of warmth. Some of the temperature -tolerant Vandas may be OK too in those lows which are rare. They'll love the humidity and the heat, put up with the occasional cold.
In case of freeze, liquid water must be continuously added to maintain temps of 32 deg F/0 deg. C. See
Ice . But I would not recommend most Cymbidiums for that climate - they need cooler nights to bloom. Some of the so-called "warmth tolerant" hybrids might work., They can certainly handle the temperatures in both directions.