Brown or black water is usually caused by sediment, rust, or mineral buildup inside your plumbing system.
Common sources include corrosion in older galvanized or iron pipes, disturbance of deposits after nearby water-main work, or a failing water heater anode rod releasing discoloration into hot-water lines.
If the issue is only on hot water, the water heater is often the culprit;
if it’s on both hot and cold, the problem may be in the main supply line or your home’s piping.