🚰
Australian Drinking Water Guidelines
Go to NHMRC's website
  • Australian Drinking Water Guidelines
  • Copyright
  • Table of updates
  • Contents
  • Figures
  • Tables
  • Boxes
  • Introduction
    • Chapter 1: Introduction
      • 1.1 Guiding principles
      • 1.2 About the Guidelines
        • 1.2.1 Scope of the Guidelines
        • 1.2.2 Purpose of the Guidelines
        • 1.2.3 Structure of the Guidelines
      • 1.3 Water quality characteristics
        • 1.3.1 Introduction
        • 1.3.2 Health-based targets
        • 1.3.3 Microbial health-based targets
        • 1.3.4 Physical and chemical guideline values
        • 1.3.5 Radiological screening and reference values
      • 1.4 Community consultation
      • 1.5 Development of the Guidelines
        • 1.5.1 Acknowledgments
      • 1.6 Future revisions of the Guidelines
      • 1.7 References
  • Part 1: Management of Drinking Water Quality
    • Chapter 2: Framework for Management of Drinking Water Quality: overview
      • 2.1 A preventive strategy from catchment to consumer
      • 2.2 Structure of the Framework
      • 2.3 Benefits of the Framework
      • 2.4 The need for multi-agency involvement
      • 2.5 Applying the Framework
      • 2.6 Correlations of the Framework with other systems
    • Chapter 3: Framework for Management of Drinking Water Quality: the twelve elements
      • 3.1 Commitment to drinking water quality management (element 1)
        • 3.1.1 Drinking water quality policy
        • 3.1.2 Regulatory and formal requirements
        • 3.1.3 Engaging stakeholders
      • 3.2 Assessment of the drinking water supply system (element 2)
        • 3.2.1 Water supply system analysis
        • 3.2.2 Assessment of water quality data
        • 3.2.3 Hazard identification and risk assessment
      • 3.3 Preventive measures for drinking water quality management (element 3)
        • 3.3.1 Preventive measures and multiple barriers
        • 3.3.2 Critical control points
      • 3.4 Operational procedures and process control (element 4)
        • 3.4.1 Operational procedures
        • 3.4.2 Operational monitoring
        • 3.4.3 Corrective action
        • 3.4.4 Equipment capability and maintenance
        • 3.4.5 Materials and chemicals
      • 3.5 Verification of drinking water quality (element 5)
        • 3.5.1 Drinking water quality monitoring
        • 3.5.2 Consumer satisfaction
        • 3.5.3 Short-term evaluation of results
        • 3.5.4 Corrective action
      • 3.6 Management of incidents and emergencies (element 6)
        • 3.6.1 Communication
        • 3.6.2 Incident and emergency response protocols
      • 3.7 Employee awareness and training (element 7)
        • 3.7.1 Employee awareness and involvement
        • 3.7.2 Employee training
      • 3.8 Community involvement and awareness (element 8)
        • 3.8.1 Community consultation
        • 3.8.2 Communication
      • 3.9 Research and development (element 9)
        • 3.9.1 Investigative studies and research monitoring
        • 3.9.2 Validation of processes
        • 3.9.3 Design of equipment
      • 3.10 Documentation and reporting (element 10)
        • 3.10.1 Management of documentation and records
        • 3.10.2 Reporting
      • 3.11 Evaluation and audit (element 11)
        • 3.11.1 Long-term evaluation of results
        • 3.11.2 Audit of drinking water quality management
      • 3.12 Review and continual improvement (element 12)
        • 3.12.1 Review by senior executive
        • 3.12.2 Drinking water quality management improvement plan
      • 3.13 References
    • Chapter 4: Framework for the Management of Drinking Water Quality: application to small water supplies
      • 4.1 Introduction
      • 4.2 Applying the Framework
        • 4.2.1 Assessment of the drinking water supply
        • 4.2.2 Preventive measures for drinking water quality management
        • 4.2.3 Implementation of operational procedures and process control
        • 4.2.4 Verification of drinking water quality
      • 4.3 Individual household supplies
      • 4.4 Reference
  • Part 2: Description of Water Quality
    • Chapter 5: Microbial Quality of Drinking Water (Updated 2022)
      • 5.1 Introduction
      • 5.2 Microorganisms in drinking water
      • 5.3 Assessing microbial risk
      • 5.4 Enteric pathogens
        • 5.4.1 Enteric pathogens of concern in drinking water
        • 5.4.2 Contamination of source waters with enteric pathogens
        • 5.4.3 Management of risk from enteric pathogens
      • 5.5 Opportunistic pathogens
      • 5.6 Cyanobacteria
      • 5.7 Nuisance organisms
        • 5.7.1 Organisms causing taste and odour problems
        • 5.7.2 Organisms causing colour problems
        • 5.7.3 Deposits due to iron and manganese bacteria
        • 5.7.4 Corrosion problems due to iron and sulphur bacteria
        • 5.7.5 Problems caused by large numbers of microorganisms
      • 5.8 References
    • Chapter 6: Physical and Chemical Quality of Drinking Water
      • 6.1 Introduction
      • 6.2 Physical quality of drinking water
        • 6.2.1 An overview of physical characteristics
        • 6.2.2 Approach used in derivation of guidelines values for physical characteristics
      • 6.3 Chemical quality of drinking water
        • 6.3.1 Inorganic chemicals
        • 6.3.2 Organic compounds (Revised 2011)
        • 6.3.3 Approach used in derivation of guideline values for chemicals
      • 6.4 Differences between Australian and WHO guideline values
      • 6.5 National and international guideline values (2016)
      • 6.6 References
    • Chapter 7: Radiological Quality of Drinking Water (Updated 2022)
      • 7.1 Introduction
      • 7.2 Sources of radiation in the environment and in drinking water
      • 7.3 Health effects of radiation
      • 7.4 Exposure to radiation
      • 7.5 Units of radioactivity and radiation dose measurement
        • 7.5.1 Units of radioactivity and radiation dose
        • 7.5.2 Converting intake to radiation dose
        • 7.5.3 Average dose of radiation
      • 7.6 Approach for derivation of reference levels and screening values for radionuclides
        • 7.6.1 System for radiation protection
        • 7.6.2 Estimation of the dose from radionuclides in water
        • 7.6.3 Estimation of risk from low-level radiation
        • 7.6.4 Reference levels and screening values for drinking water
        • 7.6.5 Application of reference levels
        • 7.6.6 Remedial measures
      • 7.7 References
    • Chapter 8: Drinking Water Treatment Chemicals (Revised 2006)
      • 8.1 Introduction
      • 8.2 Scope and limit of application of this chapter
      • 8.3 Overview of chemical treatment processes
        • 8.3.1 Control of algae
        • 8.3.2 Coagulation and flocculation
        • 8.3.3 Adsorption
        • 8.3.4 Softening
        • 8.3.5 Oxidation
        • 8.3.6 Disinfection
        • 8.3.7 Adjustment of pH
        • 8.3.8 Addition of buffering capacity
        • 8.3.9 Corrosion inhibition
      • 8.4 Public health measures
        • 8.4.1 Fluoridation
      • 8.5 Assessment of Chemicals acceptable for use in drinking water treatment (revised 2016)
        • 8.5.1 Chemicals assessed prior to 2004
        • 8.5.2 New water treatment chemicals
      • 8.6 Quality assurance for drinking water treatment chemicals
        • 8.6.1 Risks associated with drinking water chemicals
        • 8.6.2 Managing risks
        • 8.6.3 Specifications for the supply of drinking water treatment chemicals
      • 8.7 Monitoring and analytical requirements
      • 8.8 Contaminants in drinking water treatment chemicals
      • 8.9 Useful contacts
      • 8.10 References
  • Part 3: Monitoring
    • Chapter 9: Overview of monitoring (Revised 2021)
      • 9.1 Introduction
      • 9.2 Monitoring overview
        • 9.2.1 Monitoring priorities
        • 9.2.2 Principles of monitoring frequency
        • 9.2.3 Catchment-to-consumer monitoring
      • 9.3 Developing a monitoring program
      • 9.4 Operational monitoring
        • 9.4.1 Operational characteristics
        • 9.4.2 Target criteria
        • 9.4.3 Critical limits at critical control points
        • 9.4.4 Corrective action
        • 9.4.5 Operational monitoring frequency
        • 9.4.6 Chlorination as a critical control point: an example
      • 9.5 Verification of drinking water quality
        • 9.5.1 Monitoring consumer satisfaction
        • 9.5.2 Drinking water quality monitoring
      • 9.6 Water quality issues beyond the point of supply
      • 9.7 Investigative studies and research monitoring
      • 9.8 Validation of barrier performance
      • 9.9 Incident and emergency response monitoring
      • 9.10 Reliability of monitoring data
        • 9.10.1 Sample integrity
        • 9.10.2 Methods
        • 9.10.3 Detection limits
        • 9.10.4 Measurement uncertainty
        • 9.10.5 Field testing
      • 9.11 Monitoring advice for small, remote or community-managed water supplies
      • 9.12 Assessing the significance of short-term exceedances of health-based guideline values
      • 9.13 References
    • Chapter 10: Monitoring for specific characteristics in drinking water (Updated 2022)
      • 10.1 Introduction
      • 10.2 Assessing safety: short-term evaluation of monitoring
        • 10.2.1 Short-term evaluation of operational monitoring
        • 10.2.2 Short-term evaluation of drinking water quality monitoring
      • 10.3 Assessing performance: long-term evaluation of monitoring
        • 10.3.1 Long-term evaluation of microbial performance
        • 10.3.2 Long-term evaluation of health-based chemical performance
        • 10.3.3 Long-term evaluation of aesthetic performance
        • 10.3.4 Long-term evaluation of consumer satisfaction
        • 10.3.5 Improvement plan
        • 10.3.6 Performance reporting
        • 10.3.7 Summary of guideline values for microbial, chemical and physical characteristics
        • 10.3.8 Summary of reference levels and screening values for radiological characteristics
      • 10.4 Reference
  • Part 4: Information sheets
    • 1. Disinfection
      • 1.1: Introduction to water treatment
      • 1.2: Overview of disinfection
      • 1.3: Disinfection with chlorine
      • 1.4: Chloramines
      • 1.5: Disinfection with chlorine dioxide
      • 1.6: Disinfection with ozone
      • 1.7: Disinfection with ultraviolet light
      • 1.8: Other disinfectants
    • 2. Sampling
      • 2.1: Sampling Information – handling requirements and preservation
      • 2.2: Radiological monitoring and assessment of performance (updated 2022)
    • 3. Statistics
      • 3.1: Statistics – Visualising data
      • 3.2: Statistics – Assessing data
      • 3.3: Statistics – Statistical principles
      • 3.4: Statistics – Control charts and trends
      • 3.5: Number of samples required
      • 3.6: Guidance for issuing and lifting boil water advisories
      • Attachments
  • Part 5: Fact sheets
    • Microorganisms
      • Microbial indicators
        • Bacteroides
        • Coliphages
        • Clostridium perfringens
        • Escherichia coli
        • Heterotrophic plate counts
        • Intestinal enterococci
        • Thermotolerant coliforms
        • Total coliforms
      • Bacteria
        • Aeromonas
        • Burkholderia pseudomallei
        • Campylobacter
        • Escherichia coli (E. coli) (pathogenic)
        • Helicobacter pylori
        • Klebsiella
        • Legionella
        • Mycobacterium
        • Pseudomonas aeruginosa
        • Salmonella
        • Shigella
        • Vibrio
        • Yersinia
      • Protozoa
        • Acanthamoeba
        • Blastocystis
        • Cryptosporidium
        • Cyclospora
        • Giardia
        • Naegleria fowleri
      • Cyanobacteria and their toxins
        • Cyanobacteria and their toxins
        • Cylindrospermopsin
        • Microcystins
        • Nodularin
        • Saxitoxins
      • Viruses
        • Adenovirus
        • Enterovirus
        • Hepatitis viruses
        • Norovirus
        • Rotavirus
    • Physical and chemical characteristics
      • Acephate
      • Acrylamide
      • Aldicarb
      • Aldrin and Dieldrin
      • Aluminium
      • Ametryn
      • Amitraz
      • Amitrole
      • Ammonia
      • Antimony
      • Arsenic
      • Asbestos
      • Asulam
      • Atrazine
      • Azinphos-methyl
      • Barium
      • Benomyl
      • Bentazone
      • Benzene
      • Beryllium
      • Bioresmethrin
      • Boron
      • Bromacil
      • Bromate
      • Bromoxynil
      • Cadmium
      • Captan
      • Carbaryl
      • Carbendazim/Thiophanate-methyl
      • Carbofuran
      • Carbon tetrachloride
      • Carboxin
      • Carfentrazone-ethyl
      • Chloral hydrate (Trichloroacetaldehyde)
      • Chlorantraniliprole
      • Chlordane
      • Chlorfenvinphos
      • Chloride
      • Chlorinated furanones
      • Chlorine
      • Chlorine dioxide, Chlorite, Chlorate
      • Chloroacetic acids: chloroacetic acid, dichloroacetic acid (DCA), trichloroacetic acid (TCA)
      • Chlorobenzene
      • Chloroketones
      • Chlorophenols
      • Chloropicrin
      • Chlorothalonil
      • Chlorpyrifos
      • Chlorsulfuron
      • Chromium
      • Clopyralid
      • Colour (True)
      • Copper
      • Cyanide
      • Cyanogen chloride
      • Cyfluthrin, Beta-cyfluthrin
      • Cypermethrin isomers
      • Cyprodinil
      • 2,4-D [(2,4-Dichlorophenoxy) acetic acid]
      • DDT (1,1,1-trichloro-di-(4-chlorophenyl) ethane)
      • Deltamethrin
      • Diazinon
      • Dicamba
      • Dichlorobenzenes
      • Dichloroethanes: 1,1-dichloroethane, 1,2-dichloroethane
      • Dichloroethenes: 1,1-dichloroethene (1,1-DCE), 1,2-dichloroethene (1,2-DCE)
      • Dichloromethane (methylene chloride)
      • 1,3-Dichloropropene
      • Dichlorprop/Dichlorprop-P
      • Dichlorvos
      • Diclofop-methyl
      • Dicofol
      • Diflubenzuron
      • Dimethoate
      • Diquat (ion), Diquat dibromide
      • Dissolved oxygen
      • Disulfoton
      • Diuron
      • 2,2-DPA
      • Endosulfan
      • Endothal
      • Epichlorohydrin
      • EPTC
      • Esfenvalerate
      • Ethion
      • Ethoprophos
      • Ethylbenzene
      • Ethylenediamine tetraacetic acid (EDTA)
      • Etridiazole
      • Fenamiphos
      • Fenarimol
      • Fenchlorphos
      • Fenitrothion
      • Fenthion
      • Fenvalerate
      • Fipronil
      • Flamprop-methyl
      • Fluometuron
      • Fluoride
      • Flupropanate
      • Formaldehyde
      • Glyphosate
      • Haloacetonitriles
      • Haloxyfop
      • Hardness (as calcium carbonate)
      • Heptachlor and heptachlor epoxide
      • Hexachlorobutadiene
      • Hexazinone
      • Hydrogen sulfide, Sulfide
      • Imazapyr
      • Iodine, Iodide
      • Iprodione
      • Iron
      • Lanthanum
      • Lead
      • Lindane
      • Maldison (Malathion)
      • Mancozeb
      • Manganese
      • MCPA
      • Mercury
      • Metaldehyde
      • Metham
      • Methidathion
      • Methiocarb
      • Methomyl
      • Methyl bromide
      • Metiram
      • Metolachlor/s-Metolachlor
      • Metribuzin
      • Metsulfuron-methyl
      • Mevinphos
      • Molinate
      • Molybdenum
      • Monochloramine
      • Naphthalophos
      • Napropamide
      • Nicarbazin
      • Nickel
      • Nitrate and nitrite
      • Nitrilotriacetic acid (NTA)
      • N-Nitrosodimethylamine (NDMA)
      • Norflurazon
      • Omethoate
      • Organotins: dialkyltins, tributyltin oxide
      • Oryzalin
      • Oxamyl
      • Paraquat
      • Parathion
      • Parathion-methyl
      • Pebulate
      • Pendimethalin
      • Pentachlorophenol
      • Per-fluoroalkyl and poly-fluoroalkyl substances (PFAS)
      • Permethrin
      • pH
      • Picloram
      • Piperonyl butoxide
      • Pirimicarb
      • Pirimiphos methyl
      • Plasticisers
      • Polihexanide
      • Polycyclic aromatic hydrocarbons (PAHs)
      • Profenofos
      • Promecarb
      • Propachlor
      • Propanil
      • Propargite
      • Propazine
      • Propiconazole
      • Propyzamide
      • Pyrasulfotole
      • Pyrazophos
      • Pyroxsulam
      • Quintozene
      • Radionuclides, Specific Alpha and Beta Emitting
      • Radium (radium-226 and radium-228)
      • Radon-222
      • Selenium
      • Silica
      • Silver
      • Simazine
      • Sodium
      • Spirotetramat
      • Styrene (vinylbenzene)
      • Sulfate
      • Sulprofos
      • Taste and Odour
      • Temephos
      • Temperature
      • Terbacil
      • Terbufos
      • Terbuthylazine
      • Terbutryn
      • Tetrachloroethene
      • Thiobencarb
      • Thiometon
      • Thiram
      • Tin
      • Toltrazuril
      • Toluene
      • Total dissolved solids
      • Triadimefon
      • Trichlorfon
      • Trichlorobenzenes
      • 1,1,1-Trichloroethane
      • Trichloroethylene (TCE)
      • Triclopyr
      • Trifluralin
      • Trihalomethanes (THMs)
      • Turbidity
      • Uranium
      • Vernolate
      • Vinyl chloride
      • Xylenes
      • Zinc
    • Drinking water treatment chemicals
      • Aluminium chlorohydrate
      • Aluminium sulfate (alum)
      • Ammonia
      • Ammonium sulfate
      • Calcium hydroxide
      • Calcium hypochlorite
      • Calcium oxide
      • Carbon, granulated activated
      • Carbon, powdered activated
      • Chlorine
      • Copper sulfate
      • Ferric chloride
      • Ferric sulfate
      • Hydrochloric acid
      • Hydrofluorosilicic acid
      • Hydrogen peroxide
      • Hydroxylated ferric sulfate
      • Ozone
      • Polyacrylamide
      • Polyaluminium chloride
      • Polyaluminium silica sulfates
      • Polydiallyldimethylammonium chloride
      • Potassium permanganate
      • Sodium aluminate
      • Sodium bicarbonate
      • Sodium carbonate
      • Sodium fluoride
      • Sodium fluorosilicate
      • Sodium hexametaphosphate
      • Sodium hydroxide
      • Sodium hypochlorite
      • Sodium silicate
      • Sodium tripolyphosphate
      • Sulfuric acid
      • Zinc orthophosphate
  • Appendices
    • Appendix 1: Additional guidance
      • A1.1 Introduction
      • A1.2 Water supply system analysis
      • A1.3 Assessment of water quality data
      • A1.4 Hazard identification
      • A1.5 Risk assessment
      • A1.6 Preventive measures and multiple barriers
      • A1.7 Critical control points
      • A1.8 Chlorination as an example of a critical control point
      • A1.9 References
    • Appendix 2: Further sources of information on drinking water quality management
      • A2.1 Drinking water quality management - general
      • A2.2 Catchment management and source water protection
      • A2.3 Groundwater protection
      • A2.4 Risk assessment and management
      • A2.5 System analysis and management process control and optimisation
      • A2.6 Monitoring and verification
      • A2.7 Materials and chemicals
      • A2.8 Incident and emergency management
      • A2.9 Employee training and awareness
      • A2.10 Research and development
      • A2.11 Documentation and reporting
      • A2.12 Community consultation and communication
      • A2.13 Hazard analysis and critical control point (HACCP)
      • A2.14 Quality management continuous improvement
      • A2.15 Reference web sites
    • Appendix 3: Derivation of microbial treatment targets for enteric pathogens
      • A3.1 Introduction to Quantitative Microbial Risk Assessment (QMRA)
      • A3.2 Adopting the QMRA approach in the Guidelines
      • A3.3 QMRA framework for the calculation of log₁₀ reduction values (LRVs)
      • A3.4 Defining the health outcome target
      • A3.5 Selection of reference pathogens
      • A3.6 Level of reference pathogen contamination in Australian source waters
      • A3.7 Consumption volume of unheated (unboiled) water per person per day
      • A3.8 Dose response relationships
      • A3.9 Disability Adjusted Life Years (DALY) burden per case
      • A3.10 Calculation of LRVs using the QMRA framework
      • A3.11 Interpretation of calculated LRVs for practical treatment guidance
      • A3.12 Understanding log₁₀ reductions
      • A3.13 References
  • Glossary
Powered by GitBook
LogoLogo

Australian Drinking Water Guidelines 6 2011, v3.9

  • Go back to NHMRC website
On this page
  • Table A1.11 Chlorination as a critical control point
  • Process controls
  • Operational monitoring
  • Table A1.12 C.t values for inactivation by free chlorine (mg.min/L)
  • Verification
  1. Appendices
  2. Appendix 1: Additional guidance

A1.8 Chlorination as an example of a critical control point

PreviousA1.7 Critical control pointsNextA1.9 References

Last updated 6 months ago

Disinfection is designed to kill pathogenic microorganisms, thereby preventing waterborne diseases. Chlorination is the most commonly used process for disinfection; it is effective in killing bacteria and can be reasonably effective in inactivating viruses (depending on type) and most protozoa, including Giardia. Cryptosporidium is not inactivated by the concentrations of chlorine that can be safely used in drinking water.

Although the microbial quality of drinking water is of primary importance and must never be compromised, chlorine levels and the formation of chlorination byproducts should be controlled to prevent any adverse health effects that may eventually be found to be attributable to disinfection byproducts.

The effectiveness of chlorination depends on several factors, including:

  • chlorine dose

  • contact time between chlorine and the water

  • chlorine demand

  • pH

  • temperature

  • turbidity.

Chlorine demand is important because it is the chlorine residual in the water and not the chlorine dose that determines the efficacy of chlorination. Natural water contains inorganic and organic compounds that react with chlorine. Reactions with naturally occurring organic matter produce chlorination byproducts, the most well known being the trihalomethanes. Chlorine may also react with compounds such as phenols to impart a taste and odour to water.

A sufficient chlorine dose must therefore be added to the water to allow for the chlorine demand reactions to occur, and to ensure that there is an adequate free chlorine residual available to disinfect the water effectively. Turbidity should be reduced as much as possible before the addition of the disinfectant in order to decrease the chlorine demand, limit shielding of microorganisms in particles and reduce the formation potential of chlorination byproducts.

Chlorination fulfils the requirements of a critical control point. The effectiveness of eliminating potentially harmful microorganisms is validated by extensive research and technical literature (e.g. see USEPA 1999). In addition, process control measures are readily available. Chlorination must be functional and effective at all times, as even short periods of suboptimal performance can represent a serious risk to public health.

Table A1.11 and the following text provide a summary of the chlorination process as a critical control point.

Table A1.11 Chlorination as a critical control point


Process controls

Effective operation of chlorination requires consideration of several associated process control measures. These include:

  • Chlorine dosing system, ideally with flow-proportional automatic dosing and feedback loops to achieve target chlorine residual and provide rapid responses to any changes in flow and water quality. Flow meters and alarms should be provided on the chlorine feed system to warn of disinfectant loss.

  • Plant flow-rate control and the design and operation of the clear-well or post-treatment reservoir (whichever is used to provide an adequate contact time). The infrastructure for chlorination should be of sufficient capacity to handle maximum flow rates and should not be hydraulically overloaded or subjected to rapid changes in hydraulic loading, as these conditions will compromise its effectiveness.

  • pH adjustment for supplies where sudden large changes of pH are known to occur (e.g. due to problems arising from chemical dosing with lime, permanganate, caustic soda etc).

  • Provision of an alarm system on the chlorine supply, to indicate when the supply is running low, and of a spare or surplus chlorine supply. Chemical suppliers should be evaluated and selected on their ability to supply product in accordance with required specifications.

  • Inspection, calibration and maintenance of equipment to ensure continuing process capability and accuracy of monitoring results.

  • Emergency measures such as backup generators, alarms and duplicate facilities (e.g. chlorinator, disinfectant feed system, pumps, monitoring equipment etc) to avoid loss of disinfection if failure occurs.

Operational monitoring

Operational parameters

It is essential to monitor residual chlorine concentration, flow rate (contact time), chlorine dose, pH, temperature and turbidity to determine whether water is being disinfected properly. Total coliforms and heterotrophic bacteria can also be used.

For processes such as disinfection, where failure can result in a rapid change in water quality and pose a significant health risk, monitoring should be online and continuous to provide an immediate indication of performance. Flow measurement and chlorine residual can be monitored online and continuously with feedback loops to ensure correct conditions are met. For supplies where sudden changes of pH are known to occur, continuous monitoring of this parameter should also be considered. Alarm systems that are monitored 24 hours a day should be installed to indicate when operational criteria have not been met.

Critical limits and target criteria

Operational criteria for chlorination are normally determined by calculating the C.t values required to attain target levels of pathogen inactivation at specified temperatures and pH. C.t is the product of residual chlorine concentration in mg/L and the contact time in minutes.

Free chlorine residuals and C.t values should be validated for individual water supplies. Tables of C.t values for various temperatures and pHs for the inactivation of Giardia and viruses by free chlorine and other disinfectants have been published (e.g. see Table A1.12).

Ongoing compliance with minimum C.t values should be confirmed.

Table A1.12 C.t values for inactivation by free chlorine (mg.min/L)

pH
99% (2 log) inactivation 10°C
99% (2 log) inactivation 20°C
99.99% (4 log) inactivation10°C
99.99% (4 log) inactivation20°C

Giardia

7.0

75

37

150

74

8.0

108

41

216

108

Viruses

7.0

4

2

6

3

Source: USEPA (1999); Keegan et al. 2012; WaterVal 2017

Corrective action

Corrective action taken in response to target criteria or critical limits not being met could include:

  • examination of the chlorination process (investigate equipment)

  • adjustment of flow rate to increase detention time

  • adjustment of pH

  • recalculation of C.t values

  • adjustment of disinfectant dose rates

  • variation of the disinfection application point

  • verification of chlorine dose solution

  • increased sampling, verification of operational monitoring

  • inspection and calibration of equipment

  • engagement of backup chlorination equipment

  • secondary disinfection, spot dose or booster disinfection

  • water diversion or reliance on alternate supply (storage)

  • shutdown of plant, automatic immediate shutdown

  • implementation of an emergency response plan (e.g. issuing advice to boil water).

Verification

The chlorination process should be verified by supplementing with:

  • regular calibration and maintenance of the chlorine dose and monitoring equipment to ensure continuing process capability and accuracy of monitoring results. Procedures, schedules, responsibilities and records (maintenance logs) for the calibration and maintenance of equipment should be documented

  • routine sampling and testing of E. coli (or thermotolerant coliforms) in the distribution system and as supplied to consumers

  • monitoring of consumer comments and complaints regarding chlorine taste and odour

  • performance evaluation and operational audit to confirm that objectives are being met. This entails the periodic review of operational monitoring, drinking water quality monitoring data and consumer satisfaction, logbook records of planned and unplanned maintenance and calibration, and operating procedures, including microbial health-based targets.

Click for a larger version. An accessible copy of this table and a high quality PDF is available at Water Quality Guidelines resources.