Arsenic is a naturally occurring element found in the Earth’s crust, making it a common, odorless, and tasteless contaminant in groundwater. It dissolves from surrounding rock and soil formations into the water source, posing a public health concern for homeowners who rely on private wells. Unlike federally regulated public water systems, private well owners are solely responsible for ensuring their drinking water safety. Understanding safety guidelines and testing protocols is necessary because long-term consumption of even low levels of arsenic is a serious matter.
Establishing the Maximum Safe Limit
The Environmental Protection Agency (EPA) established the Maximum Contaminant Level (MCL) to define the acceptable concentration of arsenic in public drinking water systems. The MCL is currently set at 10 parts per billion (ppb), or 0.010 milligrams per liter (mg/L). This enforceable standard protects consumers from the harmful effects of long-term exposure and must be met by public water utilities.
The MCL acts only as a guideline for private well owners, as federal regulations do not mandate compliance for individual wells. The EPA also defines the Maximum Contaminant Level Goal (MCLG) for arsenic as zero. The MCLG is a health-based, non-enforceable target that reflects arsenic’s classification as a human carcinogen, representing the level where no adverse health effects would occur.
The 10 ppb limit is the primary benchmark private well owners should use when assessing water quality. If a private well test result exceeds this number, mitigation action should be taken. The World Health Organization (WHO) also recommends a provisional guideline of 10 ppb, reinforcing this international consensus.
Health Risks of Long-Term Exposure
The primary concern with arsenic in drinking water is the potential for chronic health effects from long-term, low-dose consumption. As a confirmed human carcinogen, exposure over many years increases the risk of several types of cancer. Cancers of the skin, bladder, and lung have been strongly associated with ingesting arsenic-contaminated water.
Chronic arsenic exposure is also linked to a range of systemic health issues beyond cancer. Skin changes are often the earliest non-malignant effects, including hyperpigmentation (darkening) and hyperkeratosis (thickening of the skin on the palms and soles). Cardiovascular problems, such as high blood pressure and peripheral vascular disease, have been connected to prolonged exposure.
Neurological problems, including peripheral neuropathy, have been observed in exposed populations. Research also suggests associations with conditions such as diabetes and reproductive disorders. Children are a more susceptible population because they consume more water relative to their body weight, and exposure during developmental stages can be harmful.
Testing Your Private Well Water
Because arsenic is undetectable by sight, smell, or taste, testing is the only reliable way to determine its presence and concentration. Arsenic levels in groundwater can fluctuate, making routine testing necessary for safety assurance. The initial test should be performed by a state-certified laboratory, not a home test kit, to ensure accurate results.
When collecting a sample, follow the specific instructions provided by the certified laboratory to avoid false readings. The laboratory report will provide the concentration in units like micrograms per liter (\(\mu\)g/L) or parts per billion (ppb), which are equivalent. If the initial test shows an arsenic level below 5 ppb, retesting every five years is generally recommended.
If the water contains arsenic at 5 ppb or higher, well owners should test annually, as this concentration is halfway to the regulatory MCL. Testing should also be performed immediately if any changes are made to the well structure or if water quality is suspected to have changed. Understanding the lab results in relation to the 10 ppb MCL is the first step toward mitigation strategies.
Methods for Arsenic Mitigation
Once a well test confirms arsenic contamination above the 10 ppb guideline, installing a treatment system is the most common course of action. Treatment systems are typically categorized as Point-of-Use (POU) or Point-of-Entry (POE). A POU system treats water at a single tap, usually the kitchen sink, and is suitable for treating water used for drinking and cooking.
A POE system, also known as a whole-house system, treats all the water entering the home. Whole-house treatment is generally not necessary solely for arsenic removal, as arsenic is not readily absorbed through the skin, but it may be chosen if other contaminants are present. The two most effective technologies for arsenic removal are Reverse Osmosis (RO) and Adsorptive Media Filtration.
Reverse Osmosis is a highly effective POU method that uses a semi-permeable membrane to filter out contaminants, including arsenic. Adsorptive media filtration, which uses materials like activated alumina, is effective for both POU and POE applications. This method works by chemically binding the arsenic to the media’s surface. Pretreatment may be required to convert the more difficult-to-remove form, arsenite (As(III)), into the more manageable form, arsenate (As(V)).