All about corrosivity

Science Center Objects

A U.S. Geological Survey assessment of more than 20,000 wells nationwide shows that untreated groundwater in 25 states has a high prevalence of being potentially corrosive. The states with the largest percentage of wells with potentially corrosive groundwater are located primarily in the Northeast, the Southeast, and the Northwest.

These FAQs were written in conjuction with that study.   In addition to information specific to the study, these FAQs include many answers to general corrosivity questions.

► Additional USGS Research on Corrosivity

About the Study

USGS Role Regarding Drinking Water

Human Health Implications

Information for Homeowners with private wells

Additional information on USGS assessments

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About the Study

private well

Corrosion on housing for a private well

Are the findings of this study applicable to the recent drinking water problems experienced in Flint Michigan?

No. The source of corrosive water used for the Flint drinking water supply was the Flint River, a surface-water source whereas the USGS report deals with the potential corrosivity of untreated groundwater. In addition, the high levels of lead in drinking water supplied to residents of Flint were related to inadequate treatment of the corrosive source water pumped from the Flint River by the public water utility. The USGS study is only reporting on the potential corrosivity of untreated groundwater, with the implications of having potentially corrosive water directed primarily at homeowners who rely on private wells for their drinking water supply. Unlike public water supplies like Flint, the quality and safety of drinking water from private wells are not regulated by the Federal government or, in most cases, by state laws. Rather, individual homeowners are responsible for testing, treating, and maintaining their private water systems.

What is the purpose of this study?

The purpose of this study is to present national maps of the distribution of two indicators of the corrosivity of untreated groundwater across the Nation: the Langelier Saturation Index (LSI) and the Potential to Promote Galvanic Corrosion (PPGC). The PPGC is based on chloride-to-sulfate mass ratio (CSMR). For each indicator, two maps are presented:  one map shows the values of the indicator at individual groundwater sites and, the other map shows characteristic values for each state.  The maps are based on data at about 27,000 groundwater sites obtained from the US Geological Survey’s (USGS) National Water Information System (NWIS).  The combined corrosivity index map combines the LSI and PPGC into one general indicator of potentially corrosive groundwater to summarize study results at the state level.

Why assess the potential corrosivity of the Nation’s groundwater?

Corrosive groundwater, if untreated, can dissolve lead and other metals from pipes and other components present in household plumbing.  About 43.5 million people rely upon groundwater from private wells and springs for their source of drinking water. The corrosivity of untreated groundwater is only one of several factors that may affect the quality of household drinking water at the tap. Nevertheless, it is an essential factor that should be carefully considered in testing, treating, and maintaining the quality and safety of drinking water obtained from a private water system supplied by groundwater.  

How many groundwater sites were sampled?  When were they sampled?

Water quality data from about 27,000 groundwater sites across the Nation were obtained from the U.S. Geological Survey’s National Water Information System. The samples were collected from 1991 to 2015.

What types of groundwater sites were sampled?

The study assessed corrosivity in samples from private wells, public supply wells, wells of other types, and springs.

Were the samples collected before or after treatment?

All groundwater samples were collected prior to any treatment or blending that potentially could alter the quality of the source groundwater. USGS personnel collected water samples after the well had been pumped a minimum of three casing volumes and after basic water-quality properties such as temperature, pH, and specific conductance had stabilized from outlets located before any pressure tanks or treatment systems.

Were analyses of tap water samples done as part of this study?

No. Samples were collected to represent the source of the groundwater being used for drinking water, not the quality of water at the tap.

What measures of potential corrosivity of groundwater were used in this study?

Water corrosivity is affected by more than just pH, although pH is a major driver of corrosivity in many cases. The corrosivity of water is characterized by factors such as pH, calcium concentration, hardness, alkalinity, dissolved solids, and temperature. There are several indicators of corrosivity. Two indicators are summarized in this report to provide a national characterization of the potential corrosivity of groundwater: the Langelier Saturation Index (LSI) and the chloride-to-sulfate mass ratio (CSMR). The LSI provides an indication of the extent to which calcium carbonate scale might be deposited inside pipes and other components of a distribution system (Langelier, 1936; Larson and others, 1942). In the absence of a protective scale, lead, if present, can dissolve from plumbing materials into the water (Langelier, 1936; Stumm and Morgan, 1981; Hu and others, 2012). The LSI only indicates the tendency for scaling to occur; it is not a measurement of corrosivity (Singely and others, 1984). Nevertheless, the LSI is commonly used as an indicator of the potential corrosivity of water.

A three-tier classification system based on the chloride-to-sulfate mass ratio (CSMR) developed by Nguyen and others (2010, 2011) is used to assess levels of concern related to galvanic corrosion of lead in water distribution systems. If the source water entering those systems has a relatively elevated CSMR (Gregory 1985; Edwards and Triantafyllidou, 2007; Hu and others, 2012), the potential for galvanic corrosion to occur is elevated, especially in water with low values of alkalinity (Nguyen and others (2011). In this report, untreated groundwater is assessed and the three-tier classification is applied without considering the absence or presence of lead or other metals in the distribution system. Consequently, the three-tier classification system is referred to in this report as the Potential to Promote Galvanic Corrosion (PPGC). 

The LSI and PPGC classifications are combined into a Combined Corrosivity Index to classify the potential for corrosive groundwater at the individual state scale. Confidence intervals for these classifications are provided in the report Appendix.

How can I retrieve the data used in this report?

What are the corrosivity classification uncertainties of this study?

Classification of states with respect to potential corrosivity and the Potential to Promote Galvanic Corrosion (PPGC) was based on estimates of characteristic values for the states, and those estimates are subject to uncertainty. The uncertainty associated with the estimate of the average LSI was computed using the standard confidence interval at a 90 percent confidence level (Ott and Longnecker, 2001). The uncertainty associated with estimating the proportion of groundwater sites with a given classification was computed using the Clopper-Pearson interval (Clopper and Pearson, 1934) at a 90 percent confidence level. Given a 90 percent confidence interval, six states could be given a classification that is different from the one based on the characteristic value for the state: Kentucky, Missouri, Montana, New Hampshire, North Carolina, and Vermont. Refer to the report Appendix for further discussion on the classification uncertainty.

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USGS Role Regarding Drinking Water

Is USGS responsible for monitoring drinking water?

No. The U.S. Geological Survey (USGS), and specifically, the National Water-Quality Assessment (NAWQA) Project, does not assess the quality of the Nation’s treated drinking water or conduct regulatory compliance monitoring. Rather, NAWQA assessments focus mainly on the quality of the available, untreated resource (source water), such as water upstream from treatment plants or groundwater pumped from public-supply and domestic wells.

Does USGS regulate drinking water?

No. The USGS is a non-regulatory agency under the U.S. Department of Interior and is the primary federal agency responsible for providing scientific information on the quality of the Nation’s water resources. USGS information is intended to facilitate effective management of water resources and ensure long-term availability of water that is safe for drinking and recreation and is suitable for industry, irrigation, and fish and wildlife.

Where can I learn more about how drinking water from public supplies and private wells is regulated?

The quality of finished (treated) drinking water from the Nation’s public water systems is regulated by the U.S. Environmental Protection Agency (USEPA) under the Safe Drinking Water Act (SDWA) (U.S. Environmental Protection Agency, 2004).  The SDWA defines a public water system as one that serves piped drinking water to at least 25 people or 15 service connections for at least 60 days a year (U.S. Environmental Protection Agency, 2003).  The SDWA, originally passed by Congress in 1974 and amended in 1986 and 1996, requires many actions to protect drinking water and its sources—rivers, lakes, reservoirs, springs, and groundwater.  For example, SDWA authorizes the USEPA to set national health-based standards for drinking water to protect against both naturally occurring and man-made contaminants that may be detected in drinking water (U.S. Environmental Protection Agency, 2004).  USEPA oversees the states, localities, and water suppliers who implement the drinking-water standards.  Information about how USEPA decides which contaminants to regulate, how drinking water standards are set, and the review of existing regulations is available online at: http://www.epa.gov/safewater/standard/setting.html. EPA established the Lead and Copper Rule to control levels of lead and copper in public water systems. The rule requires systems to monitor drinking water at customer taps. If lead concentrations exceed an action level of 15 ppb or copper concentrations exceed an action level of 1.3 ppm in more than 10% of customer taps sampled, the system must undertake a number of additional actions to control corrosion. If the action level for lead is exceeded, the system must also inform the public about steps they should take to protect their health and may have to replace lead service lines under their control.   See https://www.epa.gov/dwreginfo/lead-and-copper-rule for more information about the Lead and Copper Rule

The quality and safety of water from private wells are not regulated by the SDWA or, in most cases, by state laws. Rather, individual homeowners are responsible for maintaining their private well or spring systems. State laws and local regulations, where they exist, typically require a minimum amount of water testing for private wells. Regulations apply primarily at the time of well installation and are limited in scope. Less than half of the states require testing of water from new private wells, typically for bacteria and nitrate. County or other local testing requirements for new wells also may exist. Water-quality testing at the time of home sales is a condition of some home loans and is required by some states. A few states also conduct free voluntary testing programs.

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Human Health Implications

Corrosion in monitoring well

Examining corrosion inside monitoring well pipe

What are the potential human-health issues associated with corrosive well water?

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 thereby releasing metals or other contaminants that can present a human health concern. If plumbing materials contain lead, copper, or cadmium these metals may be leached into the water supply by corrosive water. Lead exposure can cause behavior problems and learning disabilities in children and can also affect the health of adults.  Per EPA drinking water guidelines,  short-term exposure to copper can cause nausea and stomach upset whereas long-term exposure may affect the liver or kidneys; long-term exposure to cadmium in drinking water can cause kidney damage.

If indicators show that my well water is potentially corrosive, will I also have high levels of lead or other metals in my well water?

Having potentially corrosive groundwater does not mean that you also have high lead or other metal levels in your tap water. It depends on several characteristics of the groundwater (pH, calcium concentration, hardness, dissolved solids, and temperature) and the materials used throughout your plumbing distribution system and if your water is untreated. The primary source of lead in private water systems are: the well pump, galvanized iron well components, brass fittings in the well and household plumbing, and leaded solder used to connect copper pipes. Knowledge of the date your well was installed and the types of materials used throughout your distribution system can help provide critical information needed to assess if what types of water-quality testing may be warranted, especially if your water is potentially corrosive.
For the issue of the potential health effects of household drinking water, the USGS looks to partner agencies at the federal and state levels to provide an indication of the potential scope of the problem. EPA’s fact sheet “Actions you can take to reduce Lead In Drinking Water http://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=20001R4V.txt” identifies steps you can take to evaluate levels of lead and copper and to reduce your exposure. Virginia and Pennsylvania are examples of two states where private water systems, 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.”(Pieper and others, 2015)

“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”.” (Swistock and others, 1993, 2009; and Swistock and Clemens, 2013)

What are the potential sources of lead in private water systems?

Lead pipe and fittings were used in homes built prior to 1930 and lead solder, which contains up to 50 percent lead and is used to connect copper pipes and fittings, was used in many homes built prior to the late 1980’s. In 1986 EPA began to regulate the amount of lead in plumbing components and lead solder. However, prior to 2014, “lead-free” brass components, in all states, except California, may have contained up to 8 percent lead. Similarly galvanized steel components may have contained from 0.5 to 1.4 percent lead prior to 2014.

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Information for Homeowners with private wells

How do I determine if my well water is corrosive?  

If plumbing materials contain lead or copper, these metals may be leached into the water supply by corrosive water. Signs of corrosive water causing leaching of metals may include bluish-green stains in sinks, metallic taste to water, and pitting or small, pinhole leaks in plumbing fixtures. You can also have your well water tested for corrosion.

Where can I find information regarding water testing, maintenance, and treatment of my well?

National Hotlines

Environmental Protection Agency Safe Drinking Water Hotline 
    1-800-426-4791  (10am  - 4pm ET, M-F)

National Ground Water Association Private Well Owner Hotline 
    855-420-9355  (10am – 4pm ET, M-F)

 

Federal Agencies

Environmental Protection Agency

    Safe Drinking Water Hotline

    Lead

    Private Drinking Water Wells

    Basic Information about Lead in Drinking Water

    Additional Information on Private Wells

    Home Water Testing

    Drinking Water From Household Wells

    Drinking Water in New England--Private Well Owners

Centers for Disease Control

    About Lead in Drinking Water

    Safe Water for Community Health (SafeWATCH)

    Private Ground Water Wells

    Drinking Water FAQ

National Institute of Health

    National Institute of Environmental Health Sciences

 

Drinking Water Organizations

National Groundwater Association:  Well Owner Information

Water Systems Council:  Well Owners' Manual

American Groundwater Trust:  The American Well Owner

Groundwater Protection Council:  Water Quality

National Rural Water Association:  Quality on Tap

Water Quality Association:  Improve Your Water

 

State Information

Alabama

    Alabama Department of Public Health: Well Water

    Alabama Extension: Drinking Water / Human Health

Alaska

    Alaska Division of Environmental Health: Drinking Water Protection

Arizona

    Arizona Department of Water Resources: Wells

    Arizona Extension: Private Wells

Arkansas

    Arkansas Department of Health: Private Water Testing.   Original link.   Organization home.

    University of Arkansas Division of Agriculture: Drinking Water

California

    California State Water Resources Control Board: A Guide for Private Domestic Well Owners

    California Environmental Protection Agency: Well Owners - Water Quality in Private Domestic Wells

Colorado

    Colorado Department of Public Health and Environment: Drinking Water: Private Wells

    Colorado State University Extension: Private Wells for Home Use

Connecticut

    Connecticut Department of Health: Private Wells

Deleware

    Deleware Health and Social Services: Drinking Water - Private Well Owners

Florida

    Florida Department of Health: Private Well Testing

Georgia

    Georgia Department of Public Health: Individual Private Wells

    University of Georgia Extension: Publications in the Household Water Quality Series

Hawaii

    Hawaii Department of Health: Safe Drinking Water

Idaho

    Idaho Department of Environmental Quality: Private Wells

    Idaho Department of Health and Welfare: Well Water Safety

Illinois

    Illinois Environmental Protection Agency: Private Well Users

    Illinois Department of Public Health: Water Wells

    University of Illinois: The Private Well Class

Indiana

    Indiana Department of Environmental Management: Private Wells and Compliant Response

    Indiana Department of Natural Resources: Water Well Record Database

Iowa

    State Hygienic Laboratory at The University of Iowa: Private Well Water

    Iowa Department of Natural Resources: Private Well Program Hot Topics

Kansas

    Kansas Department of Health and Environment: Water Well Program

Kentucky

    Kentucky Department of Environmental Protection: Groundwater Awareness

    University of Kentucky College of Agriculture, Food, and Environment: Kentucky Well Education

Louisiana

    Louisiana Department of Natural Resources: For Water Well Owners

    Louisiana Department of Health and Hospitals: Private Well Initiative

Maine

    Maine Center for Disease Control & Public Health: Well Water Maine

Maryland

    Maryland Department of the Environment: Residential Wells

    University of Maryland Extension: Wells

Massachusetts

    Massachusetts Energy and Environmental Affairs: Private Wells

Michigan

Minnesota

    Minnesota Department of Health: Water Well Information

    University of Minnesota Extension: Safe Drinking Water for Minnesotans   Original link.   Organization home

Mississippi

    Mississippi State University Extension: Protecting Your Private Well

Missouri

    Missouri Department of Natural Resources: Water Wells

    University of Missouri Extension: Drinking Water Well Management

Montana

    Montana Division of Public Health and Human Services: Private Well Testing Program

    Montana Department of Environmental Quality: Private Well Information

Nebraska

    Nebraska Department of Health and Human Services: Water Well Standards

    University of Nebraska-Lincoln: Drinking Water Testing

Nevada

    Nevada Division of Environmental Protection: Private Wells

New Hampshire

    New Hampshire Department of Environmental Services: Be Well Informed

    New Hampshire Department of Environmental Services: Private Well Testing Program

New Jersey

    New Jersey Department of Environmental Protection: General Information on Wells

    New Jersey Department of Environmental Protection, Division of Science, Research and Environmental Health: Private Well Testing Act

New Mexico

    New Mexico Environmental Public Health Tracking: Private Wells Water Quality  

    New Mexico Environment Department: Private Well Owners

New York

    New York State Department of Health: Individual Private Water Supply Wells

    Cornell University Cooperative Extension: Water Quality Information for Consumers

North Carolina

    North Carolina Health and Human Services: Well Water and Health

North Dakota

    North Dakota Department of Health: Private Water Well Construction Requirements and Private Water Well Testing

Ohio

    Ohio Department of Health: Private Water Systems

    Ohio Watershed Network: Know Your Well Water

    National Center for Water Quality Research: Well Water Testing

Oklahoma

    Oklahoma Department of Environmental Quality: Home Water Testing FAQ

    Oklahoma Water Resources Center: Drinking Water

Oregon

    Oregon Health Authority: Well Testing and Regulations

    Oregon State University: Well Water Program

    Oregon Department of Environmental Quality: Resources for Private (Domestic) Well Owners

Pennsylvania

    Pennsylvania Department of Environmental Protection: Private Water Wells

    Penn State Extension: Drinking Water Interpretation Tool

    Penn State Extension: Master Well Owner Network

Rhode Island

    URI Home*A*Syst: Private Well Testing and Protection

South Carolina

    South Carolina Department of Health and Environmental Control: Residential Wells

South Dakota

    South Dakota Department of Environment and Natural Resources: Private Well Sampling

    South Dakota Department of Health: Testing Private Wells

Tennessee

    Tennessee Department of Health: Private Water Supply

    Tennessee Department of Environment and Conservation: Well Water

Texas

    Texas Groundwater Protection Committee: Water Wells

    Texas Water Resources Institute: Texas Well Owner Network

Utah

    Utah State University Extension: Water Testing

Vermont

    Vermont Department of Health: Testing Your Drinking Water Supply

Virginia

    Virginia Department of Health: Private Well Water Information

    Virginia Household Water Quality Program/Cooperative Extension: Household Water Quality Program/Well Owner Network

Washington

    Washington State Department of Health: Drinking Water

West Virginia

    West Virginia Department of Health & Human Resources: Wells, Cisterns, and Springs   Original linkOrganization home

Wisconsin

    Wisconsin Department of Natural Resources: Information for homeowners with private wells

    University of Wisconsin Stevens Point: Homeowner Testing

Wyoming

    Wyoming Department of Environmental Quality: Know Your Well

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Additional information on USGS assessments

Where can I learn more about the quality of source groundwater for private wells and public wells across the Nation, natural and human factors that affect the quality of groundwater used for drinking water, and how groundwater-quality is changing over time?

Public Supply Wells—About 105 million people—more than one-third of the Nation’s population—receive their drinking water from one of the 140,000 public water systems across the United States that rely on groundwater pumped from wells. USGS scientists assessed water quality in source (untreated) water from 932 public-supply wells (referred to as public wells), and in finished (treated) and source water from 94 of these wells. The USGS study focused primarily on “source” water before treatment or blending and describes the occurrence of naturally occurring and man-made contaminants in source water from public wells and their potential significance to human health. USGS Circular 1346, Quality of Water from Public-Supply Wells in the U.S.

Public-Supply-Well Vulnerability—The USGS investigated public-supply-well vulnerability to contamination in 10 major metropolitan areas across the Nation to assess which contaminants in an aquifer might reach a well and when, how, and at what concentration they might arrive. Three measures are particularly useful for understanding public-supply-well vulnerability: the sources of recharge that contribute water to a well and the contaminants associated with the recharge; the geochemical conditions in the aquifer tapped by a well; and the groundwater-age mixture of the water pumped from a well. Factors Affecting Public-Supply-Well Vulnerability to Contamination

Private Wells—About 43.5 million people - or 15 percent of the Nation’s population - use drinking water from private wells, which are not regulated by the USEPA via the Safe Drinking Water Act. The USGS sampled about 2,100 private wells in 48 states from 1991 to 2004 in 30 of the Nation’s principal aquifers used for water supply. As many as 219 properties and contaminants, including pH, major ions, nutrients, radionuclides, trace elements, pesticides, volatile organic compounds, and microbial contaminants, were measured. Sampled water was taken from private wells before any home treatment. The large number of contaminants assessed and the broad geographic coverage of the study provides a foundation for an improved understanding of the quality of water from the major aquifers tapped by private wells in the United States. USGS Circular 1332, Quality of Water from Domestic Wells in Principal Aquifers of the U.S.

Water Quality in Aquifers Across the Nation—USGS scientists assessed water quality in source (untreated) water from 6,600 wells in regionally extensive aquifers that supply most of the groundwater pumped for the Nation’s drinking water, irrigation, and other uses.  The comprehensive sampling, along with detailed information on geology, hydrology, geochemistry, and chemical and water use, can be used to explain how and why aquifer vulnerability to contamination varies across the Nation. By knowing where contaminants occur in groundwater, what factors control contaminant concentrations, and what kinds of changes in groundwater quality might be expected in the future, we can ensure the future availability and quality of this vital natural resource. USGS Circular 1360, Quality of the Nation’s Groundwater

Decadal Look at Groundwater Quality— An online interactive mapping tool that provides summaries of decadal-scale changes in groundwater quality across the Nation is now available for use by the public, water-resource managers, and policy makers. The mapper shows how concentrations of 24 contaminants, such as nutrients, pesticides, metals, and volatile organic compounds, are changing over decadal periods in 67 groundwater networks across the Nation. Each network consists of about 20 to 30 wells selected to represent water-quality conditions in a given geographical area, aquifer, and in some cases, a specific land use.

Where can I learn more about the USGS National Water-Quality Assessment (NAWQA) Project?

Look online for recent NAWQA headlines, activities, and publications.
Examples of How USGS Science is Informing Groundwater Quality Management Decisions

Who do I contact for additional information about this report?

Kenneth Belitz 
Chief, Groundwater Assessment
National Water-Quality Assessment Project
kbelitz@usgs.gov

References:

Clopper, C.J., and Pearson, E.S., 1934, The use of confidence intervals or fiducial limits illustrated in the case of the binomial: Biometrika, v. 26, no. 4, p. 404–413.

Edwards, M., and Triantafyllidou, S., 2007, Chloride-to-sulfate mass ratio and lead leaching to water: Journal of American Water Works Association, v. 99, no. 7, p. 96–109.
http://www.awwa.org/publications/journal-awwa/abstract/articleid/15699.aspx

Gregory, R., 1985, Galvanic corrosion of lead in copper pipework—Phase I, measurement of galvanic corrosion potential in selected waters: Swindon, England, Water Research Centre Engineering, 74 p.

Hu, J., Gan, F., Triantafyllidou, S., Nguyen, C.K. and Edwards, M.A., 2012, Copper-induced metal release from lead pipe into drinking water, Corrosion, 68(11),  p.1037-1048. http://dx.doi.org/10.5006/0616

Langelier, W.F., 1936, The analytical control of anti-corrosion water treatment,  Journal (American Water Works Association), 28(10), p. 1500-1521.

Larson, T.E., Buswell, A.M., Ludwig, H.F. and Langelier, W.F., 1942. Calcium Carbonate Saturation Index and Alkalinity Interpretations [with Discussion]. Journal American Water Works Association, 34(11), pp.1667-1684.

Nguyen, C., Stone, K., Clark, B., Edwards, M., Gagnon, G., and Knowles, A., 2010, Impact of chloride—Sulfate mass ratio (CSMR) changes on lead leaching in potable water: Denver, Water Research Foundation, 198 p.

Nguyen, C.K., Stone, K.R., and Edwards, M.A., 2011, Chloride-to-sulfate mass ratio—Practical studies in galvanic corrosion of lead solder: Journal of the American Water Works Association, v. 103, no. 1, p. 81–92.  http://www.awwa.org/publications/journal-awwa/abstract/articleid/26682.aspx

Ott, R.L., and Longnecker, M., 2001, An introduction to statistical methods and data analysis (5th ed.): Pacific Grove, Calif., Duxbury Press, 1,152 p.

Pieper, K.J., Krometis, L.A.H., Gallagher, D.L., Benham, B.L., and Edwards, M., 2015, Incidence of waterborne lead in private drinking water systems in Virginia: Journal of Water and Health, v. 13, no. 3, p. 897–908, accessed April 6, 2016, at http://dx.doi.org/10.2166/wh.2015.275

Singley, J.E., Beaudet, B.A. and Markey, P.H., 1984. Corrosion manual for internal corrosion of water distribution systems (No. ORNL/TM-8919; EPA-570/9-84-001). Environmental Science and Engineering, Inc., Gainesville, FL (USA).

Stumm, W. and Morgan, J.J., 1981, Aquatic chemistry: an introduction emphasizing chemical equilibria in natural waters, John Wiley, New York, 780 p.

Swistock, B.R., and Clemens, S., 2013, Water quality and management of private drinking water wells in Pennsylvania: Journal of Environmental Health, v. 75, no. 6, p. 60.

Swistock, B.R., Clemens, S., and Sharpe, W.E., 2009, Drinking water quality in rural Pennsylvania and the effect of management practices: Harrisburg, Pa., Center for Rural Pennsylvania, 24 p., accessed May 10, 2016, at http://www.rural.palegislature.us/drinking_water_quality.pdf.

Swistock, B.R., Sharpe, W.E., and Robillard, P.D., 1993, A survey of lead, nitrate and radon contamination of private individual water systems in Pennsylvania: Journal of Environmental Health, v. 55, no. 5, p. 6–13.

U.S. Environmental Protection Agency, 2003, Water on tap: what you need to know: U.S. Environmental Protection Agency, Office of Water EPA 816-K-03-007, October 2003, 36p.  Available at https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P1008ZP0.TXT

U.S. Environmental Protection Agency, 2004, Understanding the safe drinking water act: U.S. Environmental Protection Agency, Office of Water EPA 816-F-04-030, June 2004, 4p.  Available at https://www.epa.gov/sites/production/files/2015-04/documents/epa816f04030.pdf