Hot water only: it's the water heater
If the brown appears only on the hot side, the tank is your source. Sediment and a spent anode rod let the tank interior corrode, and that rust comes out with the hot water. Flushing helps. If it returns quickly, the tank is corroding and replacement is on the horizon.
Cold water, first draw of the day: it's your pipes
Water sitting overnight in corroded galvanized pipe picks up rust, so the first draw runs brown and then clears. This is the classic sign of galvanized steel supply lines reaching the end of their service life. It usually arrives together with falling water pressure.
All water, all fixtures, suddenly: it's the main
Hydrant flushing, a main break or nearby construction stirs up sediment in the municipal line. It affects the whole neighborhood and usually clears within a few hours. Run a cold outside spigot for several minutes and see whether it clears.
Should you drink it?
Iron discoloration is generally an aesthetic issue rather than a health one, but discolored water is a poor thing to guess about. Avoid drinking or cooking with it until it clears, and don't wash light-colored laundry in it — iron stains fabric.
What to do next
If it's the mains, wait it out. If it's the heater, flush it. If it's the first draw from the cold side and your house still has galvanized pipe, the discoloration will keep getting worse and repiping is the real answer.
If brown water arrives with weak pressure and recurring pinhole leaks, the pipes themselves are the problem. We assess and repipe homes across Michigan. Call (888) 809-6756 any hour, or read more about Repiping in Michigan.