The water and gas can typically occupy the same trench as the electric, with some separation rules. This is typically a building/plumbing code issue. There is no NEC rule for separation.
I know plastic gas lines are yellow or have a yellow stripe. But copper painted yellow. I don't think so. Maybe a local ordinance? Never heard of this rule.assuming this work is permitted (as in done with a permit) ask the inspector there are various ways to run the gas sleeved copper comes to mind and that would work for the water also but the copper will need to be painted yellow to designate it for gas