Tap water can contain naturally occurring minerals, treatment chemicals, byproducts, and trace contaminants from source water, infrastructure, agriculture, and industry. That does not mean every substance is present in every water supply—or that detecting a contaminant automatically means the water violates a health standard.
Quick answer: The contaminants worth investigating depend on where you live, your water source, local treatment, and your home's plumbing. Start with your utility's Consumer Confidence Report and current local water-quality information. If a specific concern applies to your property, targeted testing can tell you more than appearance, taste, or a TDS meter.
Below are several regulated and emerging drinking-water concerns that consumers may encounter in water-quality reports and local investigations.
1. Arsenic
Arsenic occurs naturally in rock and soil and can enter groundwater in some regions. It can also be associated with certain industrial and historical agricultural activities. The federal maximum contaminant level for arsenic in public drinking water is 10 µg/L (10 ppb).
Long-term exposure above health-based limits is associated with serious health effects, including increased cancer risk. Private well owners in areas where arsenic occurs naturally should consider local testing guidance, as private wells are not routinely regulated like public water systems.
See our Arsenic in Drinking Water Guide.
2. Disinfection Byproducts
Chlorine and chloramine are used by water utilities to maintain disinfection. When disinfectants react with naturally occurring material in source water, they can form disinfection byproducts (DBPs), including trihalomethanes (TTHMs) and haloacetic acids (HAA5).
EPA regulates TTHMs and HAA5 because long-term exposure above the applicable standards may increase health risks. This is different from claiming that properly maintained chlorine residual itself causes the broad list of illnesses sometimes attributed to it online.
See our TTHMs Guide, HAA5 Guide, and Chlorine in Drinking Water Guide.
3. Fluoride
Fluoride can occur naturally in water, and some public water systems adjust fluoride concentrations to support dental health. At excessive long-term exposure levels, fluoride can cause dental or skeletal fluorosis.
Whether your utility fluoridates its water and the reported concentration should be available from the utility or its annual water-quality report.
See our Fluoride in Drinking Water Guide.
4. Lead
Lead usually reaches tap water through service lines, solder, fixtures, and other plumbing materials rather than being intentionally present in treated source water. Because lead cannot reliably be identified by taste, odor, or appearance, building-specific information and tap testing can matter.
Infants and children are particularly vulnerable to lead exposure. If your property may have a lead service line or older plumbing, review your utility's service-line information and testing recommendations.
See our Lead in Drinking Water Guide.
5. Herbicides and Pesticides
Agricultural and landscape chemicals can reach surface water or groundwater through runoff, infiltration, spills, and other pathways. Atrazine is one example of a regulated herbicide detected in some U.S. water sources.
Occurrence is highly location-specific, so a regional or utility report is more useful than assuming that agricultural chemicals are present in every tap water supply.
6. Mercury
Mercury can enter water from natural deposits and certain industrial or waste-related sources. EPA regulates inorganic mercury in public drinking water. Long-term exposure above the drinking-water standard can affect the kidneys.
7. Nitrate and Nitrite
Nitrate can enter groundwater and surface water from fertilizer use, septic systems, wastewater, animal waste, and natural sources. It is particularly important for private wells and agricultural regions.
EPA's federal maximum contaminant level for nitrate, measured as nitrogen, is 10 mg/L; the limit for nitrite, measured as nitrogen, is 1 mg/L. Elevated nitrate is especially important for infants because excessive exposure can interfere with the blood's ability to carry oxygen.
See our Nitrates in Drinking Water Guide.
8. PCBs
Polychlorinated biphenyls (PCBs) are persistent industrial chemicals whose manufacture was banned in the United States in 1979. Historical contamination can remain in soil, sediment, and environmental systems for long periods.
PCBs are regulated in public drinking water, but their presence is not a routine feature of every municipal supply. Local contamination history matters.
9. Perchlorate
Perchlorate occurs naturally and is also associated with products such as rocket propellants, munitions, fireworks, signal flares, and some industrial processes. It can interfere with the body's uptake of iodide, which is important for thyroid hormone production.
Current federal status: EPA proposed a national drinking-water regulation for perchlorate in January 2026. The proposed health-based Maximum Contaminant Level Goal is 20 µg/L, while EPA is considering enforceable MCL alternatives of 20, 40, or 80 µg/L. As of September 2026, this is still a proposed rule; EPA is required to sign a final rule by May 21, 2027.
10. Pharmaceuticals
Trace pharmaceutical compounds can enter wastewater through human excretion, improper disposal, manufacturing discharges, and other pathways. Wastewater treatment can reduce many compounds, but conventional treatment was not designed around every pharmaceutical substance.
Detection at trace levels does not by itself establish a health effect. This is an area where the compound, concentration, exposure, and current evidence all matter.
11. Radioactive Contaminants
Some radionuclides occur naturally in rock and groundwater, while others can be associated with human activities. EPA regulates several radiological contaminants in public drinking water, including uranium, radium, and certain beta- and photon-emitting radionuclides.
Regional geology can make radiological testing particularly relevant for some groundwater supplies.
12. Vinyl Chloride
Vinyl chloride is an industrial chemical used to manufacture PVC. In drinking-water discussions, contamination can be attributed to industrial releases and the degradation of certain chlorinated solvents in groundwater. EPA regulates vinyl chloride in public drinking water.
It is misleading to assume that ordinary household PVC plumbing automatically causes vinyl chloride contamination at the tap. Local source and contamination history are more relevant.
13. Volatile Organic Compounds (VOCs)
VOCs are a broad group of chemicals associated with fuels, solvents, industrial operations, leaking storage tanks, landfills, and other sources. Some VOCs are regulated in drinking water, while others may be monitored because of local contamination concerns.
See our VOCs in Drinking Water Guide.
14. PFAS
PFAS are a large family of synthetic chemicals used in industrial and consumer applications. Drinking-water contamination has been associated with certain manufacturing sites, airports, military facilities, firefighting-foam use, landfills, and wastewater pathways.
PFAS occurrence varies considerably by location. Check your utility and state environmental agency for current sampling information, rather than assuming that PFAS levels reported in national headlines apply directly to your home.
See our PFAS in Drinking Water Guide.
What These Contaminants Have in Common
Contaminants can enter drinking water at different points: in source water, during or after treatment, through distribution infrastructure, or through plumbing inside a property. This is why a national list cannot tell you exactly what is present at your faucet.
| Start Here | What It Can Tell You | What It May Miss |
|---|---|---|
| Consumer Confidence Report | Source water, regulated contaminants, detected levels and compliance information | Conditions unique to your building or faucet |
| Utility/state resources | Current advisories, PFAS programs, service-line information and local investigations | Some property-specific conditions |
| Targeted laboratory test | Measured results for selected contaminants at your water source or tap | Anything not included in the test panel |
| Taste, odor and appearance | Can flag changes worth investigating | Many contaminants have no detectable taste, odor or color |
Private Wells Need a Different Approach
Private domestic wells generally are not regulated under the federal Safe Drinking Water Act in the same way as public water systems. Well owners are responsible for testing and maintaining their own water supply.
Testing priorities can depend on local geology, nearby agriculture, septic systems, industry, flooding, and other conditions. State and local health departments can provide region-specific guidance.
How to Decide Whether You Need a Water Filter
Start with the contaminant rather than the filter. Review your Consumer Confidence Report, local advisories, plumbing information, and—when appropriate—targeted testing. Then compare those concerns with contaminant-specific performance evidence for the exact filtration technology and model you are considering.
No filter should be assumed to remove every contaminant. Performance depends on the filter media, design, test conditions, water chemistry, flow rate, maintenance, and the substance being evaluated.
Where Berkey® Filtration Fits
Berkey® systems are countertop gravity-fed filtration systems. Their contaminant-reduction performance depends on the specific filter elements installed, so claims should be matched to element-specific testing rather than applied to every Berkey® configuration.
Black Berkey® Elements
Black Berkey® Elements are the original primary elements used in many existing Berkey® systems. They have their own independent laboratory evidence covering a range of contaminants. Existing Black Berkey® users should evaluate Black-specific results rather than applying Phoenix certification or test data to their filters.
Phoenix Gravity New Millennium Edition™ Filter Elements
Phoenix Gravity elements are the current compatible replacement option for many Berkey® gravity-fed systems and have their own certification and independent laboratory evidence.
NSF listing: Phoenix Gravity New Millennium Edition Filter Element PGF9-2 itself is listed under NSF/ANSI 42 for chlorine reduction. NSF's listing footnote states that the component was tested to 4,000 liters for chlorine reduction and taste & odor.
Travel Berkey®, Big Berkey®, and Royal Berkey® configurations featuring Phoenix elements are separately listed under NSF/ANSI 42 for chlorine and taste-and-odor reduction, with a listed service cycle of 1,050 gallons. Those configurations are also listed under NSF/ANSI/CAN 372 for lead-content requirements.
NSF/ANSI/CAN 372 does not certify lead reduction from drinking water. PFAS, lead-reduction, chloramine, heavy-metal and other claims should be evaluated using the applicable independent laboratory evidence unless NSF specifically lists the claim.
Review the evidence for both filter families on our Berkey® Filter Test Results, or compare Berkey® water filter systems.
Final Thoughts
The most useful lesson is not that your tap water secretly contains every contaminant on this list. It is that water quality is local.
Start with your utility report and local information. Consider your building's plumbing and nearby sources of contamination. Use targeted testing when a specific concern justifies it. If filtration is appropriate, choose a system with evidence relevant to the exact contaminant you want to reduce.
For a broader reference covering lead, PFAS, arsenic, nitrates, VOCs, disinfection byproducts and other concerns, visit our Drinking Water Contaminants Reference Guide.