Drinking Water Contaminants

Arsenic may be naturally present due to arsenic-containing rocks which may leach into groundwater.  Some areas in Paulden and southern Chino Valley have very high arsenic levels in groundwater.  Some wells in the Dewey-Humboldt area exceed the arsenic Maximum Contaminant Level (MCL), and soil arsenic is very high near the Iron King Superfund site.  For more information on private wells in the Dewey-Humboldt area, see the Arizona Department of Health Services (AZDHS) publication How to Reduce Your Exposure to Arsenic and Lead in Dewey-Humboldt, Arizona. 

To meet the arsenic MCL, the City of Prescott blends water from multiple supply wells and for one production well, uses adsorptive media to meet the arsenic water quality limits.  The blending plan was approved by the Arizona Department of Environmental Quality.  The City of Prescott collects 10 arsenic samples monthly to test if levels meet regulatory limits.

CWAG and some health experts believe the City of Prescott or other suppliers should evaluate the increased costs of treatment to achieve lower arsenic levels, including near the analytical detection level of 2 or 3 parts per billion (ppb).

Chemical Symbol: As

Maximum Contaminant Level (MCL): 10 parts per billion (ppb) or micrograms per liter (ug/L)

Recommended Testing Frequency by the Arizona Department of Health Services (AZDHS): Once a new well is installed and every 5 years thereafter.

Potential Adverse Health Impacts: Large doses of inorganic arsenic can cause symptoms including nausea, vomiting, diarrhea, dehydration, and shock-impaired nerve function causing a "pins and needles" sensation in your hands and feet.  Long-term exposure to high levels of inorganic arsenic in drinking water is associated with skin disorders, an increased risk for diabetes, and high blood pressure.  Inorganic arsenic and arsenic compounds are considered to be cancer-causing chemicals and are associated with cancers of the skin, lungs, and bladder.  Arsenic is also associated with liver and kidney damage in humans.  For more information on arsenic, see:

• Centers for Disease Control and Prevention Arsenic Factsheet,
• U.S. Environmental Protection Agency (USEPA) document Arsenic Compounds, and 
• AZDHS guide What You Should Know About Arsenic in Arizona Groundwater. 

Treatment: Commonly used household filters for removal of taste, odor, and some organic compounds will not remove arsenic.  Listed as a Best Available Technology (BAT) [USEPA Drinking Water Treatability Database for arsenic], owners of private wells commonly use reverse osmosis water filtration units to reduce arsenic concentrations.  However, according to another publication, high arsenic concentrations in well water may not be reduced to safe levels using reverse osmosis (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3849398/). 

USEPA also includes other BATs for treating arsenic, e.g., ion exchange (when arsenic is in the As(V) oxidation state) and oxidation/filtration.  The oxidation/ filtration process (e.g., using ozone) converts the more toxic arsenic(III) [arsenite] to the more easily treatable arsenic(V) [arsenate].  USEPA also rates granular activated carbon filtration as effective if As(V) is present.  Before selecting a treatment technology, it is important to compare the amount and type of arsenic present in your water supply to the treatment effectiveness of each system. 

For more information on treating arsenic see the following University of Arizona Cooperative Extension publications:

• Arsenic in Private Water Wells, and
• How to Lower the Levels of Arsenic in Well Water: What Choices Do Arizona Consumers Have?

For more information on treating drinking water contaminants, see CWAG Water Quality Topic: IF I NEED TO TREAT MY PRIVATE WELL WATER, WHERE CAN I FIND GUIDANCE ON SELECTING FILTERS OR OTHER TREATMENT DEVICES?

Bacteria can enter groundwater from sewage treatment plants, septic systems, agricultural livestock operations, and wildlife.  The U.S. Environmental Protection Agency considers total coliforms a useful indicator of other pathogens in drinking water.  For example, some strains of Escherichia coli (E. coli), a strong indicator of fecal contamination, can cause serious illness and are members of the coliform group.  For public water systems, total coliforms are used to determine the adequacy of water treatment and the integrity of the distribution system. 

Maximum Contaminant Level Goal (MCLG): Zero (absent or negative) total coliform colonies per 100 milliliters (ml) of water.  An MCLG is a non-enforceable public health goal.

Recommended Testing Frequency by the Arizona Department of Health Services (AZDHS): Once a new well is installed and every year thereafter.

Potential Adverse Health Impacts: Drinking water with disease-causing bacteria, viruses, or parasites can cause gastrointestinal cramps, diarrhea, nausea, vomiting, headaches, fever, and other symptoms including even death.

Treatment: Chlorination or shock chlorination is the most widely recommended means of treating bacterial contamination in home water systems (see the University of Arizona (UofA) Cooperative Extension publications: Microorganisms in Private Water Wells and What Well Owners Should Know about Shock Chlorination).

For more information on how to correctly collect a sample, see this UofA Cooperative Extension publication: Obtaining a Water Sample for Bacterial Analysis.

Public water systems use a disinfection process to remove bacteria from drinking water.  For example, the City of Prescott utilizes chlorine for disinfection to prevent the development of bacterial contamination that could occur in the water storage and distribution system and collects 53 samples per month for total coliform tests at designated sites.

For more information on treating drinking water contaminants, see CWAG Water Quality Topic: IF I NEED TO TREAT MY PRIVATE WELL WATER, WHERE CAN I FIND GUIDANCE ON SELECTING FILTERS OR OTHER TREATMENT DEVICES?

Fluoride can be present in many aquifers and can then be found in private wells due to leaching from fluoride-rich minerals. 

Chemical Symbol: F

Secondary Maximum Contaminant Level (SMCL): 4 parts per million (ppm) or milligrams per liter (mg/L).  A SMCL is an established non-enforceable guideline.

Recommended Testing Frequency by the Arizona Department of Health Services (AZDHS): Once a new well is installed and every 5 years thereafter.

Potential Adverse Health Impacts: Fluoride may be used at low levels in toothpaste or added as a drinking water treatment to aid in dental and skeletal health.  According to the United States Environmental Protection Agency (USEPA), the target range for fluoride in drinking water is 0.7 to 1.2 ppm or mg/L (USEPA Drinking Water Treatability Database for fluoride).  But if you have children, it is particularly important to test for fluoride in your well water.  Excessive consumption of fluoride can cause skeletal fluorosis, a condition characterized by pain and tenderness of bones and joints.  Excess fluoride consumption during the formative period of tooth enamel may cause dental fluorosis (mottling discoloration of teeth) and pitting of teeth.  

Treatment: USEPA has identified the following treatment processes as Best Available Technologies for the control of fluoride in drinking water: reverse osmosis and activated alumina (USEPA Drinking Water Treatability Database for fluoride).

 For more information on treating drinking water contaminants, see CWAG Water Quality Topic: IF I NEED TO TREAT MY PRIVATE WELL WATER, WHERE CAN I FIND GUIDANCE ON SELECTING FILTERS OR OTHER TREATMENT DEVICES?

The most common sources of lead in drinking water are lead pipes, faucets, and plumbing fixtures but lead can also be found in groundwater from naturally occurring sources and past mining and smelting activities.

If you have a private well in the Dewey-Humboldt area that you use for drinking water, the Arizona Department of Health Services (AZDHS) recommends that you test it for lead (and arsenic); see the AZDHS publication How to Reduce Your Exposure to Arsenic and Lead in Dewey-Humboldt, Arizona.

Chemical Symbol: Pb

Maximum Contaminant Level Goal (MCLG): Zero.  The United States Environmental Protection Agency (USEPA) has set this level based on the best available science, which shows there is no safe level of exposure to lead.  An MCLG is a non-enforceable public health goal.

Recommended Testing Frequency by the Arizona Department of Health Services (AZDHS): Once a new well is installed.

Potential Adverse Health Impacts: Young children, infants, and fetuses are particularly vulnerable to lead because the physical and behavioral effects of lead occur at lower exposure levels in children than in adults.  A dose of lead that would have little effect on an adult can significantly affect a child.  In children, low levels of exposure have been linked to damage to the central and peripheral nervous system, learning disabilities, shorter stature, impaired hearing, and impaired formation and function of blood cells.  Lead is also harmful to adults.  Adults exposed to lead can suffer from cardiovascular effects, increased blood pressure and incidence of hypertension, decreased kidney function, and reproductive problems (in both men and women).

Treatment: Reverse osmosis or a distillation unit can remove lead from drinking water (University of Arizona Cooperative Extension publication Lead in Private Water Wells).  Activated carbon filters can also remove lead when certified for lead reduction (USEPA publication Lead Adsorption into Activated Carbon: A Critical Review of the Literature and National Sanitation Foundation (NSF) guide Certified Product Listings for Lead Reduction).

For more information see the USEPA webpage Basic Information about Lead in Drinking Water.

For more information on treating drinking water contaminants, see CWAG Water Quality Topic: IF I NEED TO TREAT MY PRIVATE WELL WATER, WHERE CAN I FIND GUIDANCE ON SELECTING FILTERS OR OTHER TREATMENT DEVICES?

Nitrate and nitrite can be present in water supplies due to agricultural activities (e.g., use of animal waste or fertilizer applications including runoff from farms), human sewage from septic systems, and erosion of natural deposits.

Chemical Symbols: NO₃ (nitrate) and NO₂ (nitrite)

Maximum Contaminant Levels (MCLs): 

• Nitrate: 10 parts per million (ppm) or milligrams per liter (mg/L)
• Nitrite: 1 ppm or mg/L

Recommended Testing Frequency by the Arizona Department of Health Services (AZDHS): Once a new well is installed and every year thereafter.

Potential Adverse Health Impacts: It is particularly important to test for nitrate in your well water if you have children.  Once taken into the body, nitrates are converted into nitrites.  High levels of nitrate and nitrite are most serious for infants.  High levels of nitrates in drinking water can cause methemoglobinemia or "blue baby syndrome."  These substances reduce the blood's ability to carry oxygen.  This acute condition can occur rapidly over days.  Symptoms include shortness of breath and blueness of the skin.  Infants under six months who drink water with high levels of nitrate can become seriously ill and die. 

Treatment: Nitrates can be removed from drinking water by reverse osmosis, distillation, or through ion exchange; see University of Arizona Cooperative Extension publications:

• Nitrate in Private Water Wells, and
• Nitrate Contamination Potential in Arizona Groundwater: Implications for Drinking Water Wells.

Note that carbon filters and standard water softeners do not remove nitrate.  Merely boiling water may increase rather than decrease the nitrate concentration.

For more information see the AZDHS guide What You Should Know About Nitrates in Arizona Private Wells.

For more information on treating drinking water contaminants, see CWAG Water Quality Topic: IF I NEED TO TREAT MY PRIVATE WELL WATER, WHERE CAN I FIND GUIDANCE ON SELECTING FILTERS OR OTHER TREATMENT DEVICES?

Radioactive contaminants such as uranium, radon, and other radionuclides can be present in groundwater due to the decay or erosion of natural deposits or can be released into the environment from human-caused sources such as uranium mining and milling.  Granitic rock and mining areas tend to have higher amounts of uranium and radon.  The presence of uranium (and thus radon) is more of a concern if you have a private well near granite deposits, e.g., the numerous granitic locations in the City of Prescott and around the border of the Prescott Active Management Area where the mountains define the edges of the Little and Big Chino Basins. 

When a drinking water well is drilled into bedrock containing uranium, the uranium can get into the well water.  When water that contains radon is used in the home, e.g., for showering, radon gas can escape from the water and become airborne.

The City of Prescott does monitor the Radionuclide Group (alpha and beta/photon emitters, combined radium 226 & 228 and uranium).  For more information on radon, see the United States Environmental Protection Agency (USEPA) webpage Radon. 

Chemical Symbol for Uranium: U

Chemical Symbol for Radon: Rn

Maximum Contaminant Level (MCL) for Uranium: 30 parts per billion (ppb) or micrograms per liter (ug/L).  There is no federal standard for radon in drinking water.

Recommended Testing Frequency by the Arizona Department of Health Services (AZDHS): Once a new well is installed and every 5 years thereafter.

Potential Adverse Health Impacts: Drinking water with radionuclides can cause toxic kidney effects and increase the risk of cancer.  Radon is a naturally occurring radioactive gas that can cause lung cancer.

Treatment: The USEPA has identified ion exchange and reverse osmosis as among the Best Available Technologies for the control of uranium in drinking water (USEPA Drinking Water Treatability Database for uranium).   

The University of Arizona Cooperative Extension publication Radon in Drinking Water and Arizona Domestic Wells provides additional information and specifies that radon can be removed from drinking water by granular activated carbon.  The publication also notes that although activated carbon is known to react with radon gas, only carbon filters that are certified (e.g., by the National Sanitation Foundation [NSF]) to reduce radon in drinking water should be used.

For more information on treating drinking water contaminants, see CWAG Water Quality Topic: IF I NEED TO TREAT MY PRIVATE WELL WATER, WHERE CAN I FIND GUIDANCE ON SELECTING FILTERS OR OTHER TREATMENT DEVICES?

Total dissolved solids (TDS) comprise inorganic salts, principally calcium, magnesium, potassium, sodium, bicarbonates, chlorides, sulfates, and some small amounts of organic matter that are dissolved in water.  Primary sources for TDS in water supplies are agricultural and urban runoff, natural sources, leaching of soil contamination, and industrial or sewage wastewater discharges.

Secondary Maximum Contaminant Level (SMCL): 500 parts per million (ppm) or milligrams per liter (mg/L).  A SMCL is an established non-enforceable guideline.

Recommended Testing Frequency by the Arizona Department of Health Services (AZDHS): Once a new well is installed.

Potential Adverse Health Impacts: Some of the biggest issues are that high TDS levels can lead to kidney stones, especially with high hard water levels, and other health problems like heart disease and diabetes.  Very hard water levels are generally considered to be above 180 ppm or mg/L of calcium carbonate (the sum of calcium and magnesium).

Treatment: Reverse osmosis is considered to be one of the best available solutions to reduce TDS levels (University of Arizona Cooperative publication Sodium in Drinking Water and Arizona Domestic Wells).

For more information on treating drinking water contaminants, see CWAG Water Quality Topic: IF I NEED TO TREAT MY PRIVATE WELL WATER, WHERE CAN I FIND GUIDANCE ON SELECTING FILTERS OR OTHER TREATMENT DEVICES?