There are two primary sources for the sediment that builds up inside water heater tanks, making water dispensed through the drain valve potentially unsafe to drink. First, while water leaving a treatment facility is microbiologically pure and free from harmful levels of contaminants, it often travels a significant distance and can potentially pick up dissolved solids, rust, lime, etc, which settles in the bottom of your tank. Second, the normal process of heating water causes heavy metals such as magnesium and calcium to precipitate out. All these contaminants settle in the bottom of your tank. When hot water is drawn out the water heater, it pulls the water from the top of the tank largely without disturbing the growing volume of anaerobic contaminants accumulating in the bottom of the tank.

The before and after photo shows water dispensed without the aid of the AquaMagic Emergency Filter and after the filter was attached. Even in desperate circumstances, you would not want to, nor would it be safe, to drink the water in your water heater—unless you are using your A300 to purify the water first.