Disinfectants

Chlorine in water reports

Chlorine is a drinking-water disinfectant used to control microbes. It is not the same topic as the disinfection byproducts HAA5 or TTHM.

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EPA dataSource review:

This is a report-reading explainer. It is not a live advisory, a household result, or a personal health assessment.

Examples on this site:
3 entries from annual water reports on this site link to this explainer.
What these results show:
Annual-report data is evidence for the named report period, not live monitoring.
Does this mean a violation?:
Not necessarily. A listed result is not automatically a violation. Check the reported value, applicable limit, report period, and status together.
Check current notices:
Current instructions must come from the water provider or another appropriate official source.

Term Identity

What the term means in an annual report

Chlorine residual is the disinfectant remaining in water after treatment and through the distribution system.

Why it may appear

Systems report disinfectant residual information to summarize report-period monitoring and the disinfectant rule context.

How it may be printed

Reports may list chlorine as Cl2, an average or range, and MRDL and MRDLG fields rather than MCL and MCLG fields.

Other names you may see
Chlorine; Chlorine as Cl2
Common report labels
Chlorine; Chlorine (as Cl2); Chlorine residual

Evidence

Official sources for this explainer

Use official federal, state, utility, or report sources before treating a page as final.

Regulatory Context

How to read the applicable rule language

Use this Chlorine context to read a report's printed fields; it does not replace the report or the current official rule.

Regulatory context

Framework

Chlorine is governed through maximum residual disinfectant level terminology and running-average compliance calculations. It remains distinct from HAA5 and TTHM, which are byproduct groups with different terms and monitoring context.

Limit or program terms

  • MRDL
  • MRDLG
  • Running annual average

Units and source context

Read whether the report uses a residual concentration, average, range, and location or distribution-system context.

What this page does not duplicate

MRDL is an enforceable residual-disinfectant term; MRDLG is a nonenforceable goal. Neither is an HAA5 or TTHM MCL.

No standalone numeric limit table is rendered here. Read the source report's printed criterion and the current official source together.

Interpretation Boundaries

What a listed result does not establish

These Chlorine boundaries apply to every report row connected to this explainer.

Household-level boundary

A system report's chlorine statistic does not establish the current residual at a particular tap.

What to verify next

  1. Check whether the row is chlorine or a disinfection byproduct.
  2. Read the reported statistic, units, period, MRDL language, and printed status together.
  3. Use provider sources for current treatment information or instructions.

Annual report examples

Examples of chlorine in water reports

Read each result with its report year, public water system, original label, units, and any printed criteria or status.

Utility report2025 report row

Chlorine (as Cl2)

From Gallup Water System's 2025 report (PWSID NM3508317). Labels, values, units, criteria, and status wording are shown as printed.

Source table
Regulated Substances
Testing or report period
2025
Reported value
Amount Detected: 1
Reported range
Range: 0.7-1
Unit printed in row
ppm
Criterion printed in row
MRDL (printed under MCL): 4; MRDLG (printed under MCLG): 4
Status printed in row
Violation: No

The row prints Year Sampled 2025 and is listed as printed.

Table note: The source table prints the 4 and 4 values beneath generic MCL and MCLG headers. This summary labels them MRDL and MRDLG to preserve the disinfectant-standard semantics used for this chlorine row.

View row in report context →Open original report
Utility report2025 report row

Chlorine

From Silver City Water System's 2025 report (PWSID NM3522609). Labels, values, units, criteria, and status wording are shown as printed.

Source table
Disinfectants and Disinfection By-Products
Testing or report period
2025
Reported value
RAA: 0.6
Reported range
Range Low-High: 0.6 - 0.6
Unit printed in row
ppm
Criterion printed in row
MRDL: 4; MRDLG: 4
Status printed in row
MEETS EPA STANDARDS: YES

The printed YES is scoped to this row and its displayed 2025 sample period.

View row in report context →Open original report
Utility report2025 report row

Chlorine

From Ruidoso Water System's 2025 report (PWSID NM3513114). Labels, values, units, criteria, and status wording are shown as printed.

Source table
Regulated Substances
Testing or report period
2025
Reported value
Amount Detected: 1.1
Reported range
Range Low-High: NA
Unit printed in row
ppm
Criterion printed in row
MRDL: [4]; MRDLG: [4]
Status printed in row
VIOLATION: No

The source prints bracketed [4] values under the MCL [MRDL] and MCLG [MRDLG] headers; they are presented as MRDL and MRDLG without changing the printed cells.

View row in report context →Open original report

Continue Reading

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