Corrosion occurs because elemental metals tend to participate in reduction/oxidation (“redox”) reactions in contact with groundwater (varying pH), resulting in the formation of stable byproducts. Corrosion in distribution systems can impact consumers' health, water treatment costs, and the aesthetics of finished water.

Corrosion tends to increase the concentration of certain metals in tap water. Two potentially toxic metals (lead and cadmium) are attributable almost entirely to leaching caused by corrosion. Three other metals – copper, iron, and zinc – cause staining of fixtures, or metallic taste, or both. The promulgation of the Lead and Copper Rule or LCR by the U.S. Environmental Protection Agency in 1991 has created an emphasis on corrosion control in domestic and public distribution and plumbing systems.

In the drinking water industry, corrosion is one of the most important problems. Small communities in the U.S. and abroad often have relatively basic (disinfection, clarification, etc.) or highly specific (metals, toxics, etc.) water quality issues, but often underutilize technologies and processes that are reliable and economic. There are various methods for controlling corrosion, including design considerations, water quality modifications, corrosion inhibitors, coatings, and linings. One common corrosion control treatment strategy is to raise the pH of the source water. The selection of a corrosion control treatment option will depend on the pH, alkalinity, dissolved inorganic carbonate (DIC), dissolved oxygen, Langelier Saturation Index, and other water quality data such as calcium, iron, manganese and orthophosphate. Invalid water quality data can result in the misapplication of a treatment strategy. This paper presents two case studies on corrosion control treatments at two small drinking water distribution systems “A” & “B” in the state of Washington. Average pH of well water at system “A” is about 6.00. Adjustment of pH with 25% wt NaOH solution is planned, as the preferred treatment based on system configuration, effectiveness, reliability, raw water chemistry, scalability, life-cycle cost comparison, and other site-specific factors. Average pH of well water at system “B” is also about 6.00. At system “B”, calcite (CaCO3) and magnesium oxide (MgO) contactors are used to neutralize pH.

Using field data, a comparison between the two processes will be made in terms of treated water quality, public health effects due to added sodium, calcium, magnesium and their significant byproducts, and life-cycle cost. This approach will help to identify which process is more sustainable by considering public health and worker safety, process economics, water quality, and any environmental impacts.