FO you could probably just use treated tap, as i dont think theres enough copper in most tap to kill verts or even shrimps(used it for my freshwater shrimp).
i had very bad luck starting my first tank with tap water, i figured how bad could it be, well i found out with all the algae issues i had that basicly killed the $700 worth of live rock i bought, ive never started another tank sence with anything but r/o and never had any of the issues i did with my first sw tank, my r/o unit was the best purchase ive ever made sence i got into the hobby