Chemistry of the Interfaces of an Electric Water Heater: Implications from an Input-Output Analysis

Abstract

Abstract In a case study, this paper responds to increasing public interest in water quality issues by investigating chemical changes as water passes through a domestic water hot water system. Elemental changes were measured by simultaneous analysis of the incoming and outgoing water streams and the deposited sediment from an electric water heater tank. The results may alter some long-held beliefs. The collected and dried sediment from the tank was analyzed for thirty common elements by inductively coupled plasma and atomic absorption techniques. Of the 25 elements found, the dominant seven in order of concentration were magnesium, aluminum, copper, zinc, manganese, iron, and sodium, as well as some surprising traces of other elements. The cold water input and the heated output were also analyzed for thirteen measurable elements. In the heated water output, magnesium had a massive 151% increase in concentration, followed by much more modest increases shown by arsenic, calcium, lead, potassium, silicon, and strontium. None of these mass balance changes compromised the potability of the water. The six elements, aluminum, boron, copper, iron, manganese, and sodium, showed decreases in aqueous concentrations on heating, thereby improving the water quality.