Contaminant explainers
Learn what these substances and measurements mean in a water report, with links to official sources. This library does not cover every contaminant.
Metals and inorganic chemicals
Named metals and inorganic chemical topics with distinct rule or action-level context.
Metals and inorganic chemicals
Lead
Lead is regulated through a treatment technique and tap-sampling action-level framework. A report row does not describe every tap or identify a home's plumbing.
Read the Lead contaminant guideMetals and inorganic chemicals
Nitrate
Nitrate is a regulated inorganic contaminant. Report labels often specify that the result is measured as nitrogen, and that basis must remain attached to the value and unit.
Read the Nitrate contaminant guideMetals and inorganic chemicals
Copper
Copper is regulated with lead under a treatment-technique and tap-sampling action-level framework. Plumbing and corrosion control can influence results.
Read the Copper contaminant guideMetals and inorganic chemicals
Fluoride
Fluoride is a regulated inorganic contaminant that can occur naturally or be adjusted by a water provider. A report result alone does not establish which source applies.
Read the Fluoride contaminant guideMetals and inorganic chemicals
Barium
Barium is a regulated inorganic contaminant. A report row supplies a system, period, unit, criterion, result, and printed status rather than a current household conclusion.
Read the Barium contaminant guideMetals and inorganic chemicals
Cyanide
The federal regulated entry is cyanide as free cyanide. A generic Cyanide report label maps here only through the reviewed row contract.
Read the Cyanide contaminant guideDisinfectants
Treatment disinfectants, kept separate from the byproducts that can form during disinfection.
Disinfectants
Chlorine
Chlorine is a drinking-water disinfectant used to control microbes. It is not the same topic as the disinfection byproducts HAA5 or TTHM.
Read the Chlorine contaminant guideDisinfection byproducts
Defined byproduct groups with report-period averaging and location context.
Disinfection byproducts
Haloacetic acids (HAA5)
HAA5 is the defined sum of five haloacetic acids formed as disinfection byproducts. It is not chlorine and it is not TTHM.
Read the Haloacetic acids (HAA5) contaminant guideDisinfection byproducts
Total trihalomethanes (TTHM)
TTHM is the defined sum of four trihalomethanes formed as disinfection byproducts. It is distinct from HAA5 and from the chlorine disinfectant.
Read the Total trihalomethanes (TTHM) contaminant guideRadionuclides
Separate activity, mass-concentration, screening, and dose concepts that must not be collapsed.
Radionuclides
Combined radium 226 and 228
Combined radium is the sum of radium-226 and radium-228 results for the federal drinking-water standard. It is not a general page for every radionuclide.
Read the Combined radium 226 and 228 contaminant guideRadionuclides
Gross alpha particle activity
Gross alpha is an activity measurement for alpha-emitting radioactivity. It does not identify one specific substance and is not equivalent to radium, beta/photon activity, or uranium.
Read the Gross alpha particle activity contaminant guideRadionuclides
Beta particle and photon radioactivity
Beta particle and photon radioactivity uses a dose-based federal standard. A 50 pCi/L gross-beta screening level is not the federal MCL.
Read the Beta particle and photon radioactivity contaminant guideRadionuclides
Uranium
Uranium is a regulated radionuclide reported as a mass concentration. It must remain separate from gross alpha activity, combined radium, and beta/photon dose context.
Read the Uranium contaminant guideMicrobial indicators
Indicator organisms and treatment-technique context, distinct from a live current-status conclusion.
Microbial indicators
Total coliform
Total coliform is a microbial indicator used to evaluate treatment and distribution-system integrity. It is not interchangeable with E. coli.
Read the Total coliform contaminant guideTreatment and operational measures
Treatment-performance terms that are not automatically contaminant concentrations.
Treatment and operational measures
Turbidity
Turbidity is a treatment and filtration performance measure, not automatically a contaminant concentration. Reports can show both an NTU result and a percentage-based treatment-technique measure.
Read the Turbidity contaminant guideUnregulated monitoring topics
Monitoring topics used to collect occurrence data without creating an enforceable federal limit.
Unregulated monitoring topics
Lithium monitoring
Lithium appears in these reports through EPA's Fifth Unregulated Contaminant Monitoring Rule. The result is monitoring evidence, not an enforceable federal drinking-water limit or violation finding.
Read the Lithium monitoring contaminant guideHow to read a water quality report
Learn where contaminant names usually appear in annual reports.
View How to read a water quality reportWater characteristics and report terms
Looking for hardness, pH, alkalinity, minerals, TDS, or secondary-standard context? Use the separate report-terms library.
View Water characteristics and report termsGuide Links
Read contaminant rows with report context
These guides help separate report detections, violation language, public notices, legal-limit fields, and public-data limitations.
How to read a water quality report
A plain-English walkthrough of Consumer Confidence Reports, including report years, detected contaminants, legal limits, violations, and source notes.
View How to read a water quality reportDetection vs. violation vs. advisory
A careful guide to three different water-record terms, what each one can mean, and what official source to check next.
View Detection vs. violation vs. advisoryWhat public water data can and cannot tell you
What official public water records can help you check, what they cannot prove, and why missing data needs cautious interpretation.
View What public water data can and cannot tell you