Selenium is a naturally occurring element that most people have never heard of, yet it may be present in your drinking water right now. Unlike more famous contaminants like lead or chlorine, selenium operates in the shadows of public awareness, even though the EPA has established strict limits to protect your health. If you've ever wondered what's really flowing from your tap, selenium deserves your attention, especially if you live in certain regions of the United States where contamination is more common.
This article explains what selenium is, where it comes from, why the EPA regulates it, and most importantly, what you can do about it in your home. Whether you're concerned about your family's long-term health or simply want to understand your water better, this guide will give you the knowledge you need to take action.
What is Selenium and Why Does It Matter in Drinking Water?
Selenium is a chemical element that occurs naturally in soil, rocks, and some foods. In small amounts, it's actually essential for human health, playing a role in thyroid function and protecting cells from damage. However, when selenium levels in drinking water become too high, it shifts from beneficial to potentially harmful.
The EPA recognizes selenium as a regulated contaminant in public water supplies. The agency set a maximum contaminant level (MCL) of 0.05 milligrams per liter (mg/L), which is 50 parts per billion (ppb). This number represents a threshold above which continued exposure poses health risks, particularly for vulnerable populations like children, pregnant women, and elderly individuals.
What makes selenium challenging is that it's invisible, odorless, and tasteless. You cannot detect it without laboratory testing. This means thousands of Americans may be unknowingly exposed to elevated selenium levels in their tap water, never realizing that a simple water quality check could reveal a problem in their home.
How Does Selenium Enter Drinking Water Supplies?
Understanding the source of selenium contamination helps explain why certain regions are more affected than others, and why this problem persists despite EPA regulations.
Agricultural Runoff and Irrigation
The most significant source of selenium in drinking water is agricultural activity. When farmers irrigate crops, water dissolves selenium naturally present in soil and carries it into groundwater and surface water supplies. This is particularly problematic in western states with extensive irrigation systems, where selenium-rich soils are common. As water evaporates from irrigation channels and fields, selenium becomes more concentrated in the remaining water, making the problem worse over time.
Industrial and Mining Discharge
Coal power plants, metal smelters, oil refineries, and mining operations discharge water containing selenium as a byproduct of their processes. When this industrial water enters nearby water sources or is treated and released into public waterways, it contributes to elevated selenium levels. Even after treatment, some selenium can persist in the water supply because standard water treatment methods don't always remove it effectively.
Natural Geological Sources
In some regions, selenium occurs naturally at high concentrations in underground rock and soil formations. Wells and groundwater sources in these areas may draw selenium-contaminated water directly from the earth. Parts of the western United States, the Great Plains, and some areas of the Midwest sit atop naturally selenium-rich geological formations, making their water supplies more vulnerable regardless of human activity.
EPA Regulation and the Maximum Contaminant Level
The EPA established its selenium MCL of 0.05 mg/L in 1994 based on decades of health research. This limit applies to all public water systems that serve 15 or more households or have at least 25 full-time residents. Public water utilities must test for selenium regularly and notify customers if levels exceed the MCL.
However, the MCL system has limitations. First, not all water systems test as frequently as optimal, so contamination can sometimes go undetected temporarily. Second, private wells and some small water systems have less stringent testing requirements. If you rely on a private well, you're responsible for testing your own water and addressing any problems you find.
The EPA's MCL is based on a lifetime exposure model, assuming an average adult drinks two liters of water daily for 70 years. For children, pregnant women, and others with different water consumption patterns or health conditions, actual safe exposure levels may differ. Using ClearWater's free ZIP code lookup at checkclearwater.com, you can quickly discover what contaminants are documented in your local water supply and which ones exceed EPA limits in your area.
Health Risks of Selenium Exposure: Both Too Much and Too Little
The relationship between selenium and human health is complex because this element serves dual roles: it's necessary in small quantities but harmful in excess.
Selenium Deficiency
When selenium intake is insufficient, the body cannot produce enough selenoprotein, a protein essential for thyroid hormone metabolism, immune function, and antioxidant defense. Selenium deficiency has been linked to Keshan disease, a type of heart condition that primarily affects children, and Kashin-Beck disease, which causes joint damage and limited mobility. These conditions are rare in developed countries but demonstrate the serious consequences of inadequate selenium.
Selenium Toxicity from Excess Exposure
Chronic exposure to elevated selenium levels causes a condition called selenosis. Early symptoms are often subtle and include hair loss, nail brittleness, gastrointestinal upset, and a distinctive garlic odor on the breath and in perspiration. More serious effects of long-term high exposure include neurological damage, kidney problems, and reproductive issues.
A landmark study conducted in Nevada during the 1980s found that people drinking water with selenium levels above 0.15 mg/L experienced increased rates of health problems. Residents reported hair loss, nail changes, and dermatological symptoms. While the EPA's MCL of 0.05 mg/L is set to prevent these effects with a safety margin, it's important to recognize that health risks increase significantly once that threshold is crossed.
Special Vulnerability in Children and Pregnant Women
Children absorb and retain selenium differently than adults, making them potentially more susceptible to its harmful effects at lower exposure levels. Pregnant women face additional concern because selenium crosses the placental barrier and accumulates in fetal tissue. High fetal selenium exposure has been associated with developmental effects and reduced birth weight in animal studies.
Parents should consider testing their home water supply if they live in areas known for selenium contamination or have a household member with health symptoms that could be related to selenium exposure, such as unexplained hair loss or brittle nails.
Which U.S. Regions Have the Highest Selenium Contamination?
Selenium contamination is not uniform across the country. Certain geographic regions face significantly higher risks based on geology, agricultural practices, and industrial activity.
Western United States
The western states, particularly California, Colorado, Utah, Wyoming, and New Mexico, consistently show elevated selenium levels in water supplies. The San Joaquin Valley in California has experienced documented selenium problems for decades due to the combination of naturally selenium-rich soils and intensive agricultural irrigation. Irrigation drainage water from this region has been so contaminated that it created severe ecological damage in wildlife refuges, with selenium concentrating in fish and waterfowl to toxic levels.
Wyoming and Colorado also report frequent selenium exceedances in both groundwater and surface water, largely due to coal mining operations and oil and gas development combined with high selenium soils.
Central United States
Parts of the Great Plains, including western Kansas, Nebraska, and Oklahoma, have documented elevated selenium in groundwater. Agricultural irrigation in these regions contributes to the problem, and the naturally high selenium content in local soils exacerbates it.
Other Affected Areas
The Upper Midwest, particularly parts of Wisconsin and Michigan, has reported selenium issues in some water systems. The Southeast generally has lower selenium levels, though localized contamination near industrial sites can occur anywhere.
If you live in any of these regions, proactive testing is wise. Even if your local water utility reports compliance with EPA limits, private well owners should arrange independent testing.
How to Test Your Water for Selenium
Testing is the first and essential step. You cannot address a problem you don't know you have.
For Public Water Customers
Public water utilities are required to provide annual water quality reports, often called Consumer Confidence Reports (CCRs). These documents list all regulated contaminants detected in the water supply and whether any exceeded EPA limits. You can request your utility's most recent report or find it online through your water provider's website.
If your utility's report shows selenium levels close to or exceeding 0.05 mg/L, or if you want independent verification, hire a certified laboratory to test a sample from your tap. The cost typically ranges from $50 to $100 for a selenium-specific test.
For Private Well Owners
You have no public agency testing your water, so you must arrange private testing. Contact your state's Department of Environmental Quality or local health department for a list of certified laboratories that perform drinking water analysis. Request testing for selenium specifically and ask for results in mg/L.
Using ClearWater for Initial Research
As a starting point, use ClearWater's free ZIP code lookup tool at checkclearwater.com to see which contaminants have been documented in your local area and how your community's water quality compares to EPA standards. This helps you understand your baseline risk level and whether selenium testing should be a priority for you.
How to Remove Selenium from Your Drinking Water
If testing reveals selenium levels above 0.05 mg/L in your water, several removal methods are effective. The best choice depends on your specific situation, water characteristics, and budget.
Reverse Osmosis Systems
Reverse osmosis (RO) is highly effective at removing selenium. An RO system forces water through a semipermeable membrane under pressure, which traps selenium and other contaminants, allowing only pure water molecules to pass through. RO systems can remove 95% or more of selenium present in water.
RO systems come in two main configurations: point-of-use (POU) systems installed under your kitchen sink, and whole-house systems. Point-of-use is less expensive and adequate for drinking and cooking water. Whole-house systems are more costly but protect all water uses. Keep in mind that RO systems produce wastewater, typically one gallon of waste for every gallon of treated water, though newer systems are becoming more efficient.
Activated Alumina Filters
Activated alumina is a specially processed form of aluminum oxide that selectively adsorbs selenium and other contaminants. When water passes through a bed of activated alumina, selenium molecules stick to the surface of the granules, removing it from the water. These filters are particularly effective for selenium removal and typically remove 90% or more of selenium present.
Activated alumina systems require regular monitoring and replacement because the filter's capacity is limited. Once saturated, the filter must be replaced. The process of removing and replacing can be messy, so this method works better for point-of-use applications rather than whole-house systems, though both are available.
Ion Exchange Resins
Ion exchange systems use specially charged resin beads that attract and trap selenium ions while releasing harmless ions in their place. These systems work well for selenium removal but are less selective than activated alumina, meaning they may also remove beneficial minerals like calcium and magnesium.
Ion exchange requires regular regeneration, a process that uses salt or other chemicals to clean and recharge the resin. This adds ongoing maintenance and chemical costs. Some people avoid ion exchange because of the salt use, though salt-free alternatives exist.
Distillation
Distillation boils water and collects the steam, leaving contaminants behind. This method removes nearly 100% of selenium and is extremely reliable. However, distillation is slow and energy-intensive, making it impractical for large water volumes. Most people use distillation only for drinking and cooking water through point-of-use units.
Combination Approaches
Many homeowners use a layered approach, combining methods for better results. For example, an activated alumina filter followed by a carbon filter captures a broader range of contaminants and provides additional polishing. Some people use a point-of-use RO system for drinking and cooking water while combining a whole-house sediment filter with other treatments for general use.
Choosing the Right Removal Solution for Your Home
Several factors should guide your decision on which removal method to use.
Water Testing Results
How far above the MCL is your selenium level? A level of 0.06 mg/L requires treatment, but a level of 0.12 mg/L demands it urgently. Additionally, test for other contaminants. If your water has multiple problems, you may need a system that addresses more than just selenium.
Your Water Usage Pattern
Do you need to treat only drinking and cooking water, or do you bathe and wash with the water too? For drinking only, point-of-use systems work fine. For comprehensive household protection, whole-house or multiple point-of-use systems are necessary.
Maintenance Commitment
RO systems need membrane replacement every 2 to 3 years. Activated alumina filters require frequent replacement. Ion exchange needs chemical regeneration. Distillers need regular cleaning. Be honest about your willingness to maintain whatever system you choose.
Budget Considerations
Initial installation costs vary widely. Point-of-use systems are less expensive upfront but may require more frequent filter changes. Whole-house systems cost more initially but may be cheaper over time if they handle multiple contaminants. Consider both upfront costs and long-term maintenance expenses.
Professional Assessment
For comprehensive guidance, hire a water treatment professional to assess your specific water composition and recommend appropriate solutions. They can perform water analysis beyond selenium and suggest systems optimized for your needs.
What If You Rent or Live in an Apartment?
Renters and apartment dwellers have fewer options but are not without solutions. Portable point-of-use systems like under-sink filters, pitcher filters, or faucet-mounted filters can reduce selenium levels for drinking water without requiring installation or landlord approval. While less comprehensive than whole-house systems, these provide meaningful protection for the water you drink and cook with.
Talk to your landlord or property management about your water quality concerns. Document any health symptoms you believe are related to water quality, and request professional water testing. In some jurisdictions, landlords have legal obligations to provide potable water meeting EPA standards.
The Bigger Picture: Staying Informed About Your Water
Removing selenium from your water solves the immediate problem, but staying informed about water quality is an ongoing responsibility. Water conditions change. New industrial facilities open. Agricultural practices shift. Aging infrastructure can introduce new contaminants.
Check your utility's annual water quality report each year. If you have a private well, test annually. Monitor news and local government reports about water quality issues in your area. If you've made improvements to your water, retest periodically to confirm your treatment system is working effectively.
Use tools like ClearWater's free ZIP code lookup periodically to update yourself on documented contaminants and trends in your local water supply. Knowledge gives you the power to protect your family's health proactively.
Takeaway: Taking Action Today
Selenium may not be the most famous drinking water contaminant, but its potential health effects make it worthy of your attention. If you live in a selenium-prone region like the western United States, or if you have unexplained health symptoms like hair loss or brittle nails, testing your water should be a priority.
Start by checking your local water utility's most recent water quality report. If your area shows any selenium detection, order a test from a certified laboratory to determine your specific exposure level. If testing confirms elevated selenium, choose a removal method that fits your living situation, water usage, and budget.
Remember that you deserve to know what you're drinking. Water quality is not something to take for granted or assume is fine without verification. With simple testing and straightforward removal options available, protecting your family from selenium contamination is entirely within your reach.