What's in Your Tap Water — Chlorine, Lead, PFAS, and the MCL Table That Shows Where EPA Limits End and Health Risk Begins

Your Tap Water Is “EPA Compliant” — but the EPA’s Legal Limit for Lead Is 667x Higher Than Its Own Health Goal of Zero

The EPA regulates drinking water through two numbers that most consumers do not distinguish: the Maximum Contaminant Level Goal (MCLG) — the level at which no known health effects occur — and the Maximum Contaminant Level (MCL) — the enforceable legal limit that balances health with treatment feasibility and cost. For many contaminants, these two numbers are dramatically different. For lead, the MCLG is zero; the action level (trigger for treatment) is 15 parts per billion (ppb). For arsenic, the MCLG is zero; the MCL is 10 ppb. For PFAS, the MCLG is zero; the enforceable limit was only established in 2024.

A water system can be in full EPA compliance while delivering water containing lead, arsenic, disinfection byproducts, and PFAS at levels that the EPA itself acknowledges carry health risk. “EPA compliant” means the water meets legal standards — it does not mean the water carries zero health risk.

This guide provides the contaminant-by-contaminant comparison: what the EPA health goal is, what the legal limit is, what typical US tap water actually contains, and what the health effects are at various concentrations.

EPA Maximum Contaminant Levels — health goals versus legal limits

Contaminant	MCLG (health goal)	MCL (legal limit)	Typical US tap water	Health effect	Common source	Detection in US water systems
Lead	0	15 ppb (action level, not MCL)	0-20 ppb (varies by plumbing)	Neurodevelopmental damage in children; kidney, cardiovascular in adults	Lead service lines, lead solder (pre-1986), brass fixtures	~10% of US systems exceed action level at some taps
Arsenic	0	10 ppb	0-50 ppb (groundwater-dependent)	Skin lesions, cancer (bladder, lung, skin), cardiovascular	Natural geological deposits; mining areas	~2,000 systems serve water >10 ppb; many more at 3-10 ppb
PFOA	0	4 ppt (2024 final rule)	0-100+ ppt (near industrial sources)	Cancer (kidney, testicular); thyroid disease; immune suppression; developmental	Industrial discharge, firefighting foam (AFFF), consumer products	Detected in ~45% of US tap water (USGS 2023 study)
PFOS	0	4 ppt (2024 final rule)	0-100+ ppt	Same as PFOA; bioaccumulative	Same as PFOA	Same as PFOA
Chromium-6 (hexavalent)	No federal MCLG (total Cr: 0.1 mg/L)	No separate federal MCL; CA proposed 10 ppb	0.03-12 ppb (EWG data)	Cancer (stomach, intestinal — Erin Brockovich contaminant)	Industrial discharge; natural deposits	Detected in 75%+ of US water systems tested
Nitrate	10 mg/L	10 mg/L	0-15 mg/L (agricultural areas)	Methemoglobinemia (blue baby syndrome) in infants <6 months	Agricultural fertilizer runoff; septic systems	5-10% of private wells exceed MCL
Trihalomethanes (THMs)	0 (carcinogen byproducts)	80 ppb (annual average)	10-80 ppb	Bladder cancer (long-term exposure); reproductive effects	Byproduct of chlorination (chlorine + organic matter)	Universal in chlorinated systems; ~4% exceed MCL
Haloacetic acids (HAA5)	0	60 ppb (annual average)	10-60 ppb	Cancer risk; reproductive effects	Byproduct of chlorination	Same — universal in chlorinated water
Chloramine	4 mg/L (MRDLG)	4 mg/L (MRDL)	0.5-4 mg/L	Respiratory irritation (dialysis patients at severe risk); taste/odor	Intentionally added as disinfectant (replacing chlorine in many systems)	~30% of US systems use chloramine
Free chlorine	4 mg/L (MRDLG)	4 mg/L (MRDL)	0.2-2 mg/L	Minimal at drinking levels; taste/odor; reacts to form THMs/HAAs	Intentionally added as primary disinfectant	~70% of US systems use chlorine
Fluoride	4 mg/L	4 mg/L (MCL); 2 mg/L (secondary standard)	0.2-1.5 mg/L (intentionally added at 0.7 mg/L target)	Dental fluorosis (cosmetic) at 2-4 mg/L; skeletal fluorosis >4 mg/L	Naturally occurring + intentional addition (fluoridation)	~73% of US population receives fluoridated water
Copper	1.3 mg/L	1.3 mg/L (action level)	0.01-1.3 mg/L	GI distress; liver/kidney damage (high exposure)	Copper plumbing corrosion	~5-10% of taps exceed action level during first-draw
Mercury (inorganic)	0.002 mg/L	0.002 mg/L	0-0.002 mg/L	Kidney damage; neurological (organic mercury is more toxic)	Natural deposits; industrial discharge	Rarely exceeds MCL in treated water
Uranium	0	30 ppb	0-30 ppb (granite regions)	Kidney toxicity; cancer risk	Natural geological deposits (granite, phosphate rock)	~4% of community systems detect uranium; mostly groundwater
Radium (226+228)	0	5 pCi/L	0-5 pCi/L	Cancer (bone, head/nasal sinus)	Natural deposits	~1% exceed MCL; concentrated in Midwest, Texas
Microplastics	No federal standard	No federal standard	0-10,000+ particles/L (limited data)	Unknown (emerging concern); possible inflammatory effects	Ubiquitous; plastic pipe leaching; environmental contamination	Detected in virtually all tap water tested (studies from 2018+)

The lead problem — why your pipes matter more than your water treatment plant

Plumbing component	Lead contribution	Homes affected	How to know	Solution
Lead service line (LSL)	Major — entire pipe from main to home is lead	~6-10 million US homes (EPA estimate)	Contact water utility; check city LSL inventory (required under 2024 Lead and Copper Rule Improvements)	LSL replacement (utility-funded or homeowner-funded depending on jurisdiction); ~$5,000-15,000 per replacement
Lead solder (pre-1986 plumbing)	Moderate — joints between copper pipes	Any home with copper plumbing installed before 1986	Year of construction; visual inspection of solder joints	Run water 30 sec - 2 min before drinking (flushes standing water); POU filter certified for lead (NSF 53)
Brass fixtures and valves	Low-moderate — brass contains up to 8% lead (pre-2014); ≤0.25% after 2014	Pre-2014 fixtures	Check fixture manufacture date; “lead-free” certification post-2014	Replace old fixtures; use cold water for drinking/cooking (hot leaches more lead)
Galvanized steel pipes	Can accumulate lead from upstream sources	Older homes with galvanized plumbing	Visual inspection (gray metal pipe, possibly corroded)	Pipe replacement; water filtration

The first-draw problem: Lead concentration in tap water is highest in the first water drawn after the water has been sitting in pipes for several hours (overnight, after work). This “first draw” has been in contact with lead-containing plumbing the longest. Running the tap for 30 seconds to 2 minutes flushes this standing water. This is a temporary measure — not a substitute for lead service line replacement or point-of-use filtration.

Lead health effects by concentration

Lead level (ppb)	EPA/WHO classification	Health effects (children)	Health effects (adults)	Action recommended
0	MCLG (health goal)	No known effects	No known effects	Ideal
1-5	Below action level	CDC: “no safe level of lead in children’s blood”; even low exposure linked to IQ reduction	Generally no detectable acute effects; long-term cardiovascular risk	Minimize exposure where feasible
5-15	Below action level (but not zero)	Measurable blood lead increases with regular consumption; developmental risk	Minimal acute risk; chronic exposure risk	Consider POU filter for households with children, pregnant women
15	EPA action level trigger	Significant concern — regular consumption raises blood lead	Kidney, reproductive, cardiovascular risk with chronic exposure	Mitigate: filter (NSF 53 for lead) or replace plumbing
15-50	Above action level	High risk — blood lead levels will rise; neurodevelopmental damage	Increased blood pressure, kidney damage	Urgent mitigation; do not drink unfiltered
>50	Severe	Very high risk	Acute toxicity possible; abdominal pain, neurological symptoms	Do not consume; bottled water + immediate plumbing investigation

PFAS — the emerging contaminant crisis

PFAS compound	EPA MCL (2024 final rule)	Previous health advisory	Detection frequency in US tap water	Half-life in human body	Primary health concerns
PFOA	4 ppt	70 ppt (2016 advisory)	~20-25% of systems tested	2-4 years	Kidney cancer, testicular cancer, thyroid disease, preeclampsia
PFOS	4 ppt	70 ppt (2016 advisory)	~20-25%	4-6 years	Same + immune suppression, cholesterol elevation
PFHxS	10 ppt (as part of mixture)	None previously	~10-15%	5-8 years	Thyroid disruption, immune effects
PFNA	10 ppt (as part of mixture)	None previously	~5-10%	2-4 years	Developmental effects, liver toxicity
PFBS	No individual MCL (hazard index approach for mixtures)	2000 ppt (2021 draft HA)	~5-10%	26 days (short-chain; rapid clearance)	Thyroid, kidney, developmental (less studied than long-chain)
GenX (HFPO-DA)	10 ppt (as part of mixture)	10 ppt (2022 advisory)	Limited data; concentrated near manufacturing sites	~3 days (rapid clearance)	Liver toxicity, kidney effects, cancer (animal studies)

The 4 ppt reality: The 2024 EPA PFAS rule set MCLs at 4 parts per trillion for PFOA and PFOS — the lowest regulatory limit the EPA has ever set for any contaminant. For context: 4 parts per trillion is equivalent to 4 drops in 100 Olympic swimming pools. Detection at this level requires advanced analytical methods (LC-MS/MS) that many water systems are still implementing. Compliance deadlines extend to 2029, meaning many systems may currently exceed the MCL without knowing it.

Disinfection byproducts — the tradeoff between microbial safety and chemical risk

Byproduct category	Individual compounds	Formation	EPA MCL	Cancer site (long-term exposure)	Risk at MCL	Risk at typical levels
Trihalomethanes (THMs)	Chloroform, bromodichloromethane, dibromochloromethane, bromoform	Chlorine + natural organic matter (humic/fulvic acids)	80 ppb (annual average of total THMs)	Bladder cancer	~1 in 10,000 excess cancer risk (EPA estimate)	~1 in 100,000 at 20-30 ppb
Haloacetic acids (HAA5)	Monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, dibromoacetic acid	Same chlorination reaction	60 ppb (annual average)	Liver, kidney cancer (animal studies)	Similar magnitude to THMs	Lower at typical levels
N-Nitrosodimethylamine (NDMA)	NDMA	Chloramine + organic nitrogen precursors	No federal MCL (CA notification level: 10 ng/L)	Liver cancer (potent carcinogen)	High per-unit risk (one of the most potent drinking water carcinogens)	Low absolute risk at ng/L levels
Chlorite	Chlorite	Chlorine dioxide treatment byproduct	1.0 mg/L	Anemia; nervous system effects (children)	Low at MCL	Generally well below MCL

The disinfection tradeoff: Chlorination saves lives — it prevents waterborne disease outbreaks (cholera, typhoid, Legionella, Giardia) that killed millions before water treatment. Disinfection byproducts are the chemical cost of that protection. The EPA MCLs balance cancer risk from DBPs against microbial risk from inadequate disinfection. Removing chlorine from tap water (via carbon filter) is appropriate at the point of use (kitchen tap) — but never at the point of entry if you are on a private system that requires disinfection.

How to read your water quality report

Information	Where to find it	What to look for	Action trigger
Consumer Confidence Report (CCR)	Mailed annually by utility; available online on utility website	All detected contaminants with levels vs. MCL	Any contaminant at >50% of MCL deserves attention
Lead and copper testing	CCR; also available by requesting your specific tap’s test (some utilities test individual homes)	90th percentile lead level; your address’s result if available	Lead >5 ppb: consider filter. >15 ppb: mitigate
PFAS testing	May not be in CCR yet (2024 rule phase-in); check utility website or state drinking water program	PFOA, PFOS, and other regulated PFAS levels	Any detection: consider RO or carbon filter; >4 ppt: mitigate
Disinfection byproducts	CCR; quarterly monitoring data if available	Total THMs (running annual average); HAA5	>40 ppb THMs or >30 ppb HAA5: consider POU carbon filter for drinking water
Hardness	CCR or utility website	mg/L as CaCO3 (soft <60; moderate 60-120; hard 120-180; very hard >180)	>120 mg/L: softener improves appliance life and soap efficiency
Well water (private)	Not regulated — YOU are responsible for testing	Bacteria (total coliform, E. coli), nitrate, pH, TDS, arsenic, lead, PFAS	Test annually for bacteria + nitrate; every 3-5 years for metals + PFAS

How to apply this

Use the ingredient-checker tool to identify treatment chemicals and their byproducts in your water — understanding whether your system uses chlorine or chloramine affects which filter technology and which byproducts to prioritize.

Read your CCR (Consumer Confidence Report). Your water utility publishes this annually — it is free, it is legally required, and it lists every contaminant detected in your water along with the level versus the MCL. Start here before buying any filter.

Test for lead at your tap. Your utility’s system-wide testing may not reflect your specific home’s plumbing. First-draw lead testing kits ($15-30, or free from many utilities) measure lead at your actual tap after water sits overnight. This is the most important single water test for homes built before 1986 or served by lead service lines.

PFAS is in nearly half of US tap water. If your utility has not published PFAS data, assume it may be present. Reverse osmosis and high-quality activated carbon filters (NSF P473 certified) are the most effective consumer-level PFAS treatments. Standard pitcher filters provide inconsistent PFAS removal.

Use cold water for drinking and cooking. Hot water leaches more lead and copper from plumbing than cold water. Always draw from the cold tap for water you will consume, even if you plan to heat it.

Private well owners: you are your own EPA. No regulatory body tests or monitors your well water. Annual testing for bacteria and nitrate, and periodic testing for metals, arsenic, and PFAS, is your responsibility. State health departments often provide low-cost or free testing programs.

Honest limitations

EPA MCLs are based on risk-benefit analysis that includes treatment cost and feasibility — they are not purely health-based numbers. MCLG values represent the health-based goal, but achieving MCLG for many contaminants (e.g., zero lead, zero THMs) is technically or economically impossible for water treatment systems. PFAS detection data is still emerging — the USGS 2023 study sampled 716 locations, which provides national estimates but not site-specific certainty. Lead testing is highly variable — a single first-draw sample may not represent average exposure, as lead levels fluctuate with water use patterns, temperature, and stagnation time. Chromium-6 has no federal MCL — the 10 ppb level referenced is California’s proposed (and litigated) state standard; most states have no chromium-6-specific regulation. Microplastic health effects are largely unknown — detection methods are not standardized, and no regulatory body has established health-based limits. DBP levels vary seasonally (higher in summer when source water organic content increases and temperatures are higher) — your CCR reports annual averages that may understate seasonal peaks. Cost estimates for lead service line replacement vary enormously by region, soil conditions, and existing infrastructure — the $5,000-15,000 range is a national average.