Yes, water shouldn't be a problem along the Pacific Coast bike route, but you may encounter an occasional smaller campsite without potable water. On a recent trip I stopped at Kirk Creek campground (in the Big Sur area) and they had signs on the water taps that it should be treated and that was also the case at some of the camps in Pt. Reyes (MTB accessible). But in general water taps with good potable water are plentiful.

The soda fountains at fast food places/convenience stores/gas stations are excellent since you can usually get ice in addition to water. A water bottle filled with ice will stay frozen for a long time when packed inside the insulation provided by a full pannier bag and can provide refrigeration for perishable food along the way. I wrap the bottle with the ice in plastic bags to protect against possible spills.