New Study Shows High Potential for Groundwater to be Corrosive in One-Half of U.S. States

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A recent U.S. Geological Survey (USGS) assessment of more than 20,000 wells nationwide indicates that groundwater in 25 States and the District of Columbia has a high potential for being naturally corrosive. The States with the largest percentage of wells with potentially corrosive groundwater are located primarily in the Northeast, the Southeast, and the Northwest.

Image shows a map of all 50 states color-coded for their potential for groundwater corrosivity

The prevalence of potential corrosive groundwater was highest in 25 States in the Northeast, Southeast, and Northwest. About 24 million people in these States and the District of Columbia are dependent on private water systems for drinking water. Credit: Figure 6 from Belitz and others, 2016.

In the United States, water used for public supply is regulated and often is treated to control corrosion, metal contamination, and other undesirable qualities. In contrast, self-supplied water is not generally regulated and often is not treated. Approximately 44 million people are self-supplied and depend on domestic wells or springs for their water supply.

The corrosivity of water is one of many factors that can affect the presence of lead and other metals in household water supplies. Naturally corrosive water is not dangerous to consume by itself; however, if left untreated, corrosive water can dissolve lead and other metals from pipes and other components in water distribution systems and potentially lead to human exposure through drinking water.

Two indicators of potential corrosivity—the Langelier Saturation Index (LSI) and the Potential to Promote Galvanic Corrosion (PPGC)—were used to identify which areas in the United States might be more susceptible or less susceptible to elevated concentrations of metals in household drinking water. The prevalence of potentially corrosive groundwater by State was evaluated by combining the two indicators into a combined index.

Potentially corrosive groundwater is present in all 50 states and the District of Columbia. It is important to understand the potential corrosivity of groundwater because metals like lead can be leached from pipes into the water supply by corrosive water. The findings have the greatest implications for homeowners with private drinking water systems that are not routinely monitored or treated for corrosivity.

For concerns about potential health effects of household drinking water, the USGS looks to Federal and State agencies to provide an indication of the potential scope of the problem.

The USGS National Water-Quality Assessment Project provided the funds for the study.