According to plumbing industry sources, up to 90 percent of residential water heaters built between 1993 and 1996 have a defective polypropylene “dip tube” inside the unit. Dip tubes are designed to deliver cold water to the bottom of the water heater so it does not mix with the already heated water in the upper portion of the unit. These defective dip tubes break down inside the water heater and cause plastic chips to flow through water faucets. These chips do not pose a health risk, but they can decrease water flow from household faucets and appliances and diminish water heater efficiency and effectiveness. If you experience this problem, contact your water heater manufacturer for replacement information.