The Analytical Side to Compliance with Drinking Water Regulations

Sep 24, 2012

Sewage treatment

Two new U.S. Federal regulations went into effect in 2009 that directly impact drinking water utilities that use chemical disinfection. Specifically, the Ground Water Rule and the EPA Method 334.0 are now in place with the purpose of improving the quality of drinking water. This paper summarizes the key elements of the new regulations and describes how they affect utilities’ daily operations, plus it will provide a comparison of available technologies for monitoring and calibration equipment as they relate to the regulations.

© Siemens Water Technologies Corp.

The intent is a balanced and clear understanding of the regulations and to help utility managers make smarter equipment choices to optimize operations while staying in compliance.


Ground Water Rule

The U.S. EPA promulgated the final Ground Water Rule (GWR) in October 2006 to reduce the risk of exposure to fecal contamination that may be present in public water systems that draw from ground water sources. The EPA originally proposed the GWR in May 2000. The rule establishes a risk targeted strategy to identify ground water systems at high risk for fecal contamination. Requirements for compliance monitoring began on December 1, 2009.
More specifically, for compliance monitoring of ground water systems that use chemical disinfection, the Rule states the following based on number of people served:
  • More than 3,300 people continuously monitor their disinfection concentration and maintain the minimum disinfectant residual concentration determined by the state.
  • 3,300 people or fewer take daily grab samples or meet continuous monitoring requirements described above for those serving more than 3,300 people.

U.S. EPA Method 334.0

In November 2009, the U.S. EPA published Method 334.0 “Determination of Residual Chlorine in Drinking Water using an on-line Chlorine Analyzer” (1). This method is for the analysis of residual chlorine (free or total) in drinking water and is primarily intended to be used by utilities for compliance with daily monitoring requirements.
Interestingly, this method allows for the use of any type of on-line chlorine analyzer including amperometric and DPD based instruments for compliance monitoring when used in conjunction with a grab sample reference method that is approved for compliance monitoring. This includes both the DPD colorimeters as well as amperometric titrators.
In summary, EPA method 334.0 stipulates the following:
  • Plant personnel must have a thorough knowledge of the equipment being utilized including its operation, maintenance and calibration.
  • Plant personnel must document proof of this knowledge by a required initial demonstration of capability for use of both the grab sample measurement equipment as well as the on-line analyzer.
  • Perform initial calibration of the grab sample method equipment throughout the range of use or perform a single calibration with a NIST traceable primary standard if the instrument is factory certified.
  • Establish the frequency between needed calibration checks of the on-line analyzer with a rigorous initial testing procedure.
  • If the on-line analyzer chlorine reading is not within +/- 0.1 mg/l or +/- 15% of the grab sample measurement, the following steps must be taken:
    • Verify the calibration of the grab sample instrument using NIST traceable primary chlorine standards.
    • Calibrate the on-line analyzer.

Finding the Right Solution

Utility operators are extremely busy tending to many tasks and customer needs during any working day. For this reason alone, it is important that compliance with regulations does not interfere with other routine responsibilities.
There are several factors to consider when determining how to adopt and adapt with the least impact on daily operations. Compliance with the new regulations requires an on-line analyzer, a grab sample instrument and a thorough understanding of the procedures. Finding the right solution consists of:
  • Selecting the most appropriate on-line analyzer for your needs
  • Selecting the most suitable grab sample measurement instrument for your needs
  • Having access to step-by-step guides for the above instruments written specifically for the new regulations

Selecting the on-line analyzer

There are a number of important criteria that should be considered to ensure that the best fitting on-line analyzer is placed into service. The chart below illustrates the differences between amperometric and colorimetric (a.k.a. DPD) analyzers.

Differences between amperometric and colorimetric (DPD) analyzers.

Criteria Comparison
Disinfection control
Amperometric analyzers provide continuous measurement, allowing for accurate dosing control.
DPD analyzers provide an analysis every three minutes, which is difficult to use for accurate dosing control.
Life cycle costs
Amperometric analyzers do not require reagents to operate, so there are no recurring costs.
DPD instruments require reagents for every analysis, usually performed every three minutes, and therefore have higher life cycle costs.
Sanitary sewer
Amperometric analyzer sample waste stream does not require a sanitary sewer discharge.
DPD on-line analyzer sample waste is required to be discharged to a sanitary sewer.
Accuracy Both measurement technologies provide the required accuracy.
Variations in pH
Amperometric analyzers have several simple options: use a membrane style sensor; a pH compensated bare electrode sensor; or a chemically buffered bare electrode sensor.
DPD analyzers do not require pH compensation because the sample is chemically buffered.
High levels of iron and/or manganese
Amperometric analyzers are not greatly affected by metals except when they are present at high concentrations.
DPD analyzers are prone to metal fouling and interferences.
Calibration data storage While this is not specifically instrument-dependent, the ability to store and recall previous calibration data is an easy and effective diagnostic tool.
As you can see from the table, the differences in accuracy, variations in pH and the ability to store calibration data are minor. Albeit, the sanitary sewer requirements of the DPD analyzers may not be a deal breaker for one analyzer over another, but, the fact is, it is a requirement and may affect small or remote treatment plants.
The larger differences come into play concerning the recurring chemical costs (life cycle) and real-time analysis for precise control. DPD analyzers require reagents that must be purchased, stocked and replenished in the analyzer. This adds expense and takes time. Similarly, DPD analyzers provide chlorine residual measurements once every three minutes, which makes dosing control difficult, inefficient and poses a risk of over feeding and under feeding the disinfectant.
Lastly, many ground water sources do have elevated levels of iron and manganese, which present treatment challenges beyond the on-line analyzer. Since DPD analyzers rely on colorimetric measurement, both iron and manganese will interfere with the measurements and more routine maintenance (cleaning) of the sample cell will be required.
For the majority of the criteria listed above, amperometric analyzers are the best suited for residual chlorine measurement. The Depolox ® 3 plus Residual Analyzer is one such example, which has low life cycle costs, provides real-time analysis for accurate dosing control and also includes the ability to store calibration data for improved diagnostics.

Selecting the grab-sample instrument

The choice of grab sample measurement instrumentation is equally important, and again, the application criteria should be closely matched to your needs. There are two types to consider: amperometric titrators and colorimetric (hand-held) instruments.

Comparison betwen amperometric titrators and colorimetric (hand-held) instruments.

Criteria Comparison
Amperometric titrators are by far more accurate than colorimetric instruments.
Hand-held instruments provide the accuracy required for meeting the EPA Method.
Easy of use
Amperometric titrators require specialized expertise and are more complex to use than colorimetric instruments.
Hand-held instruments that are certified by the manufacturer are easiest to use as they require a minimum of up-front calibration. If not certified by the manufacturer, they require extensive calibration at the plant prior to use.
Life cycle costs
Amperometric titrators are certainly more expensive than hand-held instruments for both capital and on-going costs.
Primary standards for calibration
Amperometric titrators do utilize stock solutions but require specialized expertise.
Hand-held instruments utilize prepared solutions that require dilution and mixing.
Beware; most primary standards have batch-to-batch concentration variations that require dilution calculations, use specialized glassware, and undergo extra washing and rinsing procedures, all of which take extra time.
For grab sample measurement instruments, the choice really comes down to simplicity versus extreme accuracy. Amperometric titrators are capable of analysis down to 1 ppb, but require specialized equipment, skills and therefore have higher life cycle costs. The accuracy of hand-held instruments is much lower, but they still meet the requirements of the U.S. EPA Method and have lower life cycle costs (equipment, reagents, labor).
For the majority of utilities, hand-held instruments are the best suited for grab sample measurement. The P334 Colorimeter is one such example, which comes with a factory certified calibration curve, to save time, and employs a simple and reliable primary chlorine standard reference, eliminating the need for specialized glassware, calculations and extra procedures.

For utilities that already employ titrators, such as the Series A790, they may be perfectly comfortable with those and there is no need to change. However, it may be advantageous to have a hand-held device to meet the added requirements of the Method.

Note: Colorimetric color wheels do not provide the accuracy required to meet the EPA Method and are therefore not permitted.

Access to step-by-step guides

Although the required steps to calibrate and maintain a specific on-line analyzer are covered in detail in the analyzer’s instruction manual, the new method takes the procedural requirements for the operation and calibration of both the on-line analyzer and grab sample measurement instrument a step further to ensure proper operation.
Without a pragmatic approach to the use of on-line analyzers that is compliant with the Method 334.0, a utility operator may well be overwhelmed with the new requirements stipulated. To minimize the impact to operations, a complete solution on how to comply is therefore critical.
Such a procedure manual should guide the operator through the following steps:
  • Procedure for the initial verification of the colorimeter or titrator
  • Initial demonstration of capability for either a colorimeter or titrator
  • Initial grab sample comparison testing required to put the on-line analyzer in use for compliance monitoring
  • Establishing frequency of routine analyzer checks
  • Routine comparison check for on-line chlorine analyzer
With a step-by-step procedure manual written specifically to help guide you through the procedural requirements for compliance, you will spend less time worrying about and calibrating your on-line analyzer and more time making sure your plant is running efficiently.


The importance of providing a continuous supply of safe drinking water cannot be understated. Both the Ground Water Rule and EPA Method 334.0 help to raise the bar in drinking water quality. Although they present additional procedural requirements on utilities, the proper equipment choice and a pragmatic approach to its use make compliance with regulations achievable with minimal interruption.

About the author

Stephan Andrée is an expert in disinfection instrumentation solutions for Siemens Water Technologies. He has more than 21 years of experience in water treatment technologies with positions in sales, electronics design, new product development and product management. Mr. Andrée can be reached at


Ground Water Rule: Federal Register Vol. 71, No. 216, November 8, 2006, pages 65573-65660
EPA Method 334.0: Federal Register Vol. 74, No. 216, November 10, 2009, page 57910
1. U.S. EPA Method 334.0: Determination of Residual Chlorine in Drinking Water using an On-Line Chlorine Analyzer


More News and Articles


Siemens Water Technologies Corp.

Stephan Andrée

181 Thorn Hill Road

15086 Warrendale, PA

United States


+1 (724) 772-1402



To website