National Water-Quality Assessment (NAWQA) Program
The prevalence of potentially corrosive groundwater is rated high to very high in 25 states and the District of Columbia. About 24 million people in these areas rely upon groundwater from private water systems for their source of drinking water.
The combined corrosivity index map combines the Langelier Saturation Index and the Potential to Promote Galvanic Corrosion (based on the chloride-to-sulfate mass ratio) into one general indicator of potentially corrosive groundwater to summarize study results at the state level.
Naturally corrosive water is not dangerous to consume by itself. Nevertheless, it can cause health-related problems by reacting with pipes and plumbing fixtures in homes. If plumbing materials contain lead or copper, these metals may be leached into the water supply. Signs of corrosive water causing leaching of metals may include bluish-green stains in sinks, metallic taste to water, and pitting or small leaks in plumbing fixtures.
The Langelier Saturation Index (LSI) provides an indication of the extent to which calcium carbonate scaling may occur inside pipes and other components of plumbing systems. If no scaling occurs, the water can be considered corrosive, thus the LSI is often used as a general indicator of the corrosivity of water.
Groundwater in 25 states and the District of Columbia was characterized as potentially corrosive. The corrosivity of groundwater within a state was characterized on the basis of the average LSI. About 24 million people within these 25 states rely upon groundwater from private water systems for their source of drinking water.
The corrosiveness of water was characterized at 20,962 groundwater sites nationwide and included private wells, public supply wells, other well types, and springs:
Potential Corrosive - 32 percent of the groundwater sites
Indeterminate - 63 percent of the groundwater sites
Scale Forming - 5 percent of the groundwater sites.
The chloride-to-sulfate mass ratio (CSMR), along with alkalinity, is used to classify concerns related to the potential for galvanic corrosion in water distribution systems. Galvanic corrosion of lead is an electrochemical process that can occur when lead pipe or lead solder is in contact with a dissimilar metal such as copper. Elevated CSMRs can increase the potential for galvanic corrosion of the plumbing system. If these systems contain lead or other metals, these metals could be released into the water. CSMR is referred to as the potential to promote galvanic corrosion (PPGC) because untreated groundwater was assessed without considering the absence or presence of lead in the distribution system.
Groundwater in 11 states and the District of Columbia is characterized as having a high potential to promote galvanic corrosion. Groundwater in 33 states is characterized as moderate potential. About 42 million people within these combined 44 states rely upon private groundwater systems for their source of drinking water.
The potential to promote galvanic corrosion is characterized at 26,632 groundwater sites nationwide and included private wells, public supply wells, other well types, and springs:
High Concern - 8 percent of the groundwater sites
Moderate Concern - 67 percent of the groundwater sites
Low Concern - 26 percent of the groundwater sites
Virginia and Pennsylvania are examples of two states where private water sources, such as wells, springs, or cisterns, are especially common. Private water systems are used by about 1.7 million people in Virginia and about 3 million people in Pennsylvania.
In these states, the Virginia Household Water Quality Program and the Pennsylvania Master Well Owner Network provide practical information to homeowners
about maintaining, testing, and protecting private water systems.
University researchers at Virginia Tech and Penn State work with these specialized programs to monitor the quality of drinking water supplied by private water systems and to provide testing and advice to identify and remediate water-quality problems caused by contaminated or corrosive groundwater.
“Between 2012 and 2014, we found that 19% of the 2,144 private water systems sampled in Virginia exceeded the EPA lead action level of 15 μg/L,” said Dr. Kelsey Pieper, USDA-NIFA Postdoctoral Fellow at Virginia Tech. “We also observed that ‘lead-free’ plumbing components released lead when exposed to more corrosive groundwater supplies.”
“In Pennsylvania, corrosive water is usually associated with certain types of bedrock geology but can be found across the entire state,” said Bryan Swistock, a water resources specialist with Penn State Extension. “Lead levels exceeded the EPA action level in 12 percent of the 251 drinking water systems monitored in Pennsylvania in 2007”.”
For additional information, contact:
Chief, Groundwater Assessment
National Water-Quality Assessment Project