Does homeowners insurance cover plumbing repairs in Costa Mesa?

Usually the damage, not the pipe. A worn or corroded pipe is maintenance and its repair is the homeowner's cost everywhere. The sudden water damage a burst pipe causes (floors, walls, belongings) is commonly covered, subject to your deductible, which is why documenting the event promptly matters. Sewer backups are different again: they are commonly excluded from the base policy and covered only by a sewer backup endorsement, typically inexpensive relative to one backup. Ask your insurer about the endorsement before you need it, not after.