Information on key US EPA drinking water regulations.

Drinking Water FAQs

What is the Stage 1 D/DBP Rule?

On December 16, 1998, the US EPA published the Stage 1 Disinfectants/Disinfection By-Products (D/DBP) Rule. A summary is available at www.awwa.org.

This rule is the result of regulatory negotiations that began in 1992. The Stage 1 D/DBP Rule applies to community water systems (CWSs) and non-transient-noncommunity water systems (NTNCWSs) that use chemical disinfection for water treatment. Additionally, transient-noncommunity water systems (TNCWSs) that use chlorine dioxide are also affected.

The rule sets maximum residual disinfectant level goals (MRDLGs), maximum residual disinfectant levels (MRDLs) for disinfectants (see tables below), maximum contaminant level goals (MCLGs) and maximum contaminant levels (MCLs).

MRDLG and MRDLs for Disinfectants
Disinfectant Residual MRDLG (mg/L) MRDL (mg/L)
Chlorine as free Cl2 4 4.0
Chloramine as total Cl2 4 4.0
Chlorine as total ClO2 0.8 0.8
Source:  AWWA Journal

MCLGs and MCLs for Disinfectants
Disinfection By-Product MCLG (mg/L) MCL (mg/L)
Total trihalomethanes (THMs) n/a 0.080
Chloroform (CHCl3) 4 4.0
Bromodichloromethane (CBrCl2) 0  
Dibromochloromethane(CBr2Cl) 0.06  
Bromoform(CHCl3Cl)    
Haloacetic acids n/a 0.06
Dichloroacetic acid
 0  
Trichloroacetic 0.3  
Chlorite 0.8 1.0
Bromate 0 0.010
Source:  AWWA Journal
TOC analysis is an approved analytical method as stated in part 5310 of Standard Methods. Part 5310-C specifically relates to TOC analyzers with UV-persulfate or heated persulfate oxidation methods. 5310-B and 5310-D are high-temperature combustion oxidation and wet-chemical oxidation respectively (see below for more information on 5310C).

What is Subpart H?
Subpart H of 40 CFR141 details requirements for filtration and disinfection. Most importantly it classifies which PWS facilities must comply based upon water sources and populations served. Examples of regulated entities are public water systems that treat surface water and serve >100,000, and public water systems that treat ground water and serve >50,000. Details of which facilities are regulated are available in the EPA’s 40 CFR141 Federal Register here: (notice in PDF format).

Compliance dates for Subpart H:

  • Large Subpart H systems—3 years after promulgation of the D/DBP Rule (December 2001).
  • Small Subpart H systems—5 years after promulgation (December 2003).
  • All Groundwater systems—5 years after promulgation (December 2003).method?

What are Disinfection Byproducts (DBPs)?
DBPs (e.g. chloroform, bromoform, etc.) are produced from the reaction of organic materials or compounds in municipal waters with chemical disinfectants (e.g. chlorine, chloramines, hypochlorite etc.). Trihalomethanes (THMs) are the most widely known/studied of these due to their toxic/carcinogenic effects on mammals. The formation of THMs occurs when water systems are treated with halogenated disinfectants like chlorine:

The addition of chlorine to water produces hypochlorous acid:
Cl2 + H2O -> HCl + HOCl

The hypochlorous acid then ionizes to hypochlorite:
HOCl <-> H+ + OCl-

Organic matter exists in ground and surface water due to biological decomposition. Leaves and grass for instance form methane gas as a decomposition by-product, and animal decay produces both fulvic and humic acids. This “natural” organic matter in the water system may be “halogenated” by the hypochlorous acid (or hypochlorite) to produce disinfection byproducts (DBPs) like chloroform and chloroacetic acid:

HOCl + CH4 -> CHCl3 (chloroform)

HOCl + CH3COOH -> CCl3COOH (chloroacetic acid)

In an effort to minimize the levels of toxic/carcinogenic DBPs in municipal water systems, the levels of Total Organic Carbon (TOC), or disinfection byproduct precursors, is being thoroughly studied.

What is ASTM D 5904-96 standard test method?
Title: ASTM 5904-96 — Standard Test Method for “Total Carbon, Inorganic Carbon and Organic Carbon in Water by Ultraviolet, Persulfate Oxidation and Membrane Conductivity Detection.”

This method covers the determination of TC, IC and TOC over the range of 500 ppb – 30 ppm. The method utilizes UV/Persulfate oxidation and the membrane conductivity detection system that is a patented Ionics Instruments technology. The Method may be obtained at www.astm.org.

What is ASTM D 5997-96 standard test method?
Title: ASTM 5997-96 — Standard Test Method for “On-Line Monitoring of Total Carbon, Inorganic Carbon in Water by Ultraviolet, Persulfate Oxidation, and Membrane Conductivity Detection.”

ASTM D 5997-96 details the standard test method for on-line analysis of total carbon and inorganic carbon in water using UV/persulfate oxidation, and membrane conductivity detection. The methodology described employs Ionics Instruments patented membrane technology for determining TC, IC and TOC over the range of 0.05 – 50,000 ppb. The Method may be obtained at www.astm.org.

What is ASTM D 6317-98 standard test method?
Title: ASTM 6317-98 — “Standard Test Method for Low Level Determination of Total Carbon, Inorganic Carbon and Organic Carbon in Water by Ultraviolet, Persulfate Oxidation, and Membrane Conductivity Detection.” (See www.standardmethods.org.)

ASTM D 6317-98 details the standard test method for laboratory or grab-sample analysis of total carbon and inorganic carbon in water using UV/persulfate oxidation, and membrane conductivity detection. The methodology described employs Ionics Instruments patented membrane technology for determining TC, IC and TOC over the range of 10.0–1,000 ppm. The Method may be obtained at www.astm.org.

What is Standard Methods part 5310 C?

The Standard Methods part 5310 C (of Part 5000 – Aggregate Organic Constituents) is the method of Total Organic Carbon (TOC) analysis by “Persulfate-Ultraviolet or Heated Persulfate Oxidation Method.” (See www.standardmethods.org.)

In addition to high-temperature combustion (part 5310 B) and wet-chemical oxidation (part 5310 D), UV/Persulfate is an accepted method for the analysis of TOC in water.

High-temperature combustion had formerly been accepted as the method of choice for TOC analysis. Recent independent studies have shown that “Selective membrane-based conductometric detection, when combined with an inorganic carbon remover module and UV-persulfate oxidation, gave results comparable to other technologies over a wide range of environmental samples.”1

The UV/Persulfate oxidation method has been shown to be comparable to the other methods in most cases, and actually more suitable for many. The convenience and ease of use of the Sievers model 800 makes it the choice of many leading municipal laboratories for their TOC testing needs.

1Kaplan, Louis A., Comparison of three TOC methodologies, Journal AWWA, 92/4:149