Thanks so much for your input. Below are additional useful points from EPA guidelines.
BASIC INFORMATION ABOUT DRINKING WATER DISINFECTION
4) What disinfectants are available for drinking water?
Most water utilities use chlorine as a primary disinfectant because of its effectiveness in killing potentially harmful organisms.
• Chlorine is effective in killing bacteria, viruses, and other potentially harmful organisms in water.
• One disadvantage of chlorine is it can react with natural organic matter present in water to form potentially harmful disinfection byproducts.
• Water utilities sometimes use chlorine several times during treatment because the initial dose loses its effectiveness over time.
Monochloramine is commonly used as a secondary disinfectant to protect the water as it travels from the treatment plant to consumers.
• Monochloramine is effective in killing bacteria, viruses, and other potentially harmful organisms but takes much longer to act than chlorine.
• One disadvantage of monochloramine is it can react with natural organic matter present in water to form potentially harmful disinfection byproducts.
• Monochloramine is more chemically stable than chlorine, which makes it longer lasting and an effective secondary disinfectant.
Water utilities may use ozone, UV light, or chlorine dioxide as primary disinfectants in the treatment plant.
• Ozone, UV light, and chlorine dioxide are effective in killing bacteria, viruses, and other potentially harmful organisms in water at the treatment plant.
• One disadvantage of ozone, UV light, and chlorine dioxide is they do not provide protection as water travels through pipes.
• Either chlorine or monochloramine should still be used in addition to any primary treatment process to protect the quality of treated water as it travels from the treatment plant to the customer.
Additional Supporting Information:
1. See question 3 for a discussion of primary and secondary disinfectants. See questions 5
and 6 for a specific discussion of chlorine and monochloramine as a primary and secondary
disinfectant.
2. Potentially harmful organisms include disease-causing bacteria, viruses, and protozoa.
Chlorination and chloramination are not effective at inactivating Cryptosporidium. EPA
requires that utilities that use surface water test and treat for Cryptosporidium where
necessary.
3. Natural Organic Matter: Complex organic compounds that are formed from decomposing
plant, animal and microbial material in soil and water. They can react with disinfectants to
form disinfection by products. Total organic carbon (TOC) is often measured as an indicator
of natural organic matter
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Osama Ali
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Original Message:
Sent: 02-03-2026 10:03
From: Brian Krieger
Subject: drinking water disinfection
Hi Osama, I've seen this paper below on water treatment which might give you more information that I am able to off the top of my head. But in evaluating the treatment method, you would also need to consider the volume, location, cost and hazards associated with the treatment method. For example, Chlorine (Cl2 or Hypo) are a really common treatment method. And I understand that it works well and is economic. But chlorine gas releases from the drums present very real hazards for the operators and the surrounding built environment. UV light is also very effective, but it requires power. So, when there is no power or limited it doesn't work so well.
I'm not an expert in the most common use in Australia, but hypochlorite and chlorine gas are the two most common methods I am aware of. Chlorine gas has an increasing role due to the ease of use and being able to store large amounts allowing water purification to continue during longer term flooding. It's also a cheaper to transport, but significantly more dangerous in an incident involving the drums.
Evaluating Disinfection Techniques of Water Treatment Using Multi-Criteria Decision-Making Method Chapter First Online:
Also, the NHMRC has a good overview here: 1.2: Overview of disinfection | Australian Drinking Water Guidelines
Hope that helps a bit, it's a broad question with many challenges.
Cheers Brian.
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Brian Krieger
Chief Advisor Major Amusement Park Licensing
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