Natural sea water here is not viable.
Though I haven't tested the water quality of the coast/bays here, I don't think the water quality is good enough to sustain a reef tank without consistent hair algae blooms/poor coral health. I don't know of any person that straight up pulls water from the ocean. If you go down to Los Angeles and San Diego they can use seawater directly from the ocean. But I don't recommend doing it here.
Neptune Aquatics uses natural sea water but I believe it is filtered.
BUT i could be wrong. Let's wait to see who chimes in.
@BAYMAC would know.
This is kinda off topic but in Santa Barbara (near Los Angeles area) they have a spigot on the UCSB campus where you can get Natural Salt Water for free. Peep this thread.
http://reefcentral.com/forums/showthread.php?t=541355