[Khoas]

Here in Adelaide most CP will die in about 4 - 6 weeks on tap water due to salt build up. With Nepenthes they tolerant tap water but do better on rain water. If you water from above and keep the plants out of trays they will handle hard water better because alot of the salt gets washed out.
I would say Heliamphora do prefer R/O water, one of our members only uses R/O water for his heli and they are truely massive.