Jeffrey. PEX is a great product and dirt cheap compared to copper. Copper has gotten better. I don't see Mexican copper in any of my supply houses anymore. I think they all learned there lesson. Its not how aggressive the water is. It comes down to the quality of the pipe and fittings. Also electrolysis and grounding. As a plumber you know the old school way of grounding a house was through the copper pipes. That is no longer allowed in California. However I have been in houses and buildings that are grounded to the copper and you can actually put a volt meter on a bathroom angle stop and get low voltage ground readings. Hope helps.
I read your post on copper pinholes. I heard of a lot of homes repiped in la county as well that werent very old (mid 80s to mid 90s). I heard it was poor water quality in Santa clarita? So here is my question. Whats your recomended solution to your area and general so cal. If you belive the pipe was bad then do you recomend copper repipe? Plastic Pex or cpvc. Personaly I do only copper but I do mainly commercial construction (when I have work) and a variety of service (when I have to)