Water heater manufacturers cannot guarantee against rusty water because of the number of factors that are involved beyond the manufacturer’s control.
A water heater tank is the primary water reservoir in the home. (Toilet tanks also act as reservoirs) Any contamination that exists in the incoming water will finally settle in the storage tank.
Water mains are constructed of steel or cast iron pipe. Even though rust is not readily detected in the incoming cold water, a great amount of rust particles can be filtered out through large volume use.
The water heater tank acts as a water filter, and the many thousands of gallons that pass through the system over the years deposit all the rust or other foreign particles into the tank. It is for this reason that a water heater should be periodically flushed out through the drain valve provided at the bottom of the heater.
Experience shows that a great majority of so-called rusty water conditions are not rust, but sand and clay sediment which finds its way into the water heater through well systems utilized in many homes, or from major water main breaks which would result in great quantities of clay and mud getting into the main system while the mains are under repair.
This same problem exists in new housing developments where a lot of clay and other earth materials lay in the pipes before they are connected to the water system and then these materials are washed into all the homes that are being supplied by these mains.
Occasionally, water utility companies will flush their systems for routine maintenance and fire department activity at hydrants in the neighborhood will usually stir up sediment as well.
A possible remedy for any of the above conditions is to drain the tank and thoroughly flush the inside surface.