Table of Contents
Executive Summary
Sydney Water’s 2024–2025 nitrification control program — switching from monochloramine to free chlorine across 14 reservoirs serving approximately 105,000 customers — is one of the more ambitious disinfectant management trials run in Australia. Presented at the 2026 AWA/IWA Young Water Professionals Conference in Melbourne (5–6 August), the program shows that system-wide disinfectant switching is technically feasible, but only with continuous monitoring infrastructure to run it safely and document what happened.
For a board, the takeaway is simple. Disinfectant switching is not a treatment plant adjustment. It is a system-wide operational event that touches water quality at every point from the plant to the customer tap. Investment in continuous inline residual chlorine and pH monitoring — supplied by Shanghai ChiMay through Modbus-integrated transmitter networks — is the difference between a controlled, documented intervention and an uncontrolled risk event.
The Strategic Context
What Nitrification Does to a Distribution System
Nitrification — ammonia-oxidising bacteria consuming ammonia and producing nitrite — undermines the basic purpose of a drinking water distribution system: holding safe disinfectant residuals from plant to tap. When nitrification takes hold:
- Disinfectant residuals drop below protective levels
- Nitrite accumulates, and nitrite is a regulated parameter
- Biofilm regrowth potential rises
- Customer confidence in water quality erodes
For a system serving 105,000 customers across 14 reservoirs, nitrification is not an academic concern. It is an operating reality that has to be managed.
Sydney Water’s Approach
The strategy was straightforward in concept and very complex in execution: switch temporarily from monochloramine to free chlorine, flush ammonia out of the system, starve the nitrifying bacteria, then return to monochloramine once biological pressure is suppressed.
Doing it required:
– Stopping ammonia dosing at treatment plants
– Passing all 14 reservoirs through breakpoint chlorination
– Purging pipelines of monochloramine-dominated water
– Strategic flushing to draw free chlorine through the entire network
– Gradually increasing chlorine set points to limit taste and odour impacts
– Continuous monitoring at multiple points across the network
– Coordination across operational teams and the system operations centre
What the Data Showed
Trial 1 (2024): The Learning Experience
The first attempt did not reach Sydney Water’s internal 90% disinfection target. Nitrification was suppressed during the free chlorine phase, but the effect proved temporary — as warmer conditions returned, nitrification recurred at customer taps first and then at reservoirs.
That result was not a failure. It was the information that shaped the redesign.
Trial 2 (2025): The Improved Approach
The 2025 redesign incorporated three changes:
– Higher starting chlorine set points — more aggressive breakpoint chlorination
– Deeper reservoir cycling — more thorough flushing of stored water
– Detailed coordination with the system operations centre — decisions made in real time off continuous monitoring data
Nitrite was effectively removed. Customer impacts stayed limited. No biofilm sloughing was observed. Winter came out as the preferred operating window.
Michael Ray’s conclusion: “The free chlorine trial could be an effective strategy for managing disinfection in a heavily nitrified distribution system.”
The Board-Level Case for Continuous Monitoring Investment
Risk Management
Running a system-wide disinfectant switch without continuous monitoring is an unacceptable operational risk. The procedure involves:
– Changing the fundamental chemistry of water that reaches 105,000 customers
– Running breakpoint chlorination through infrastructure designed for monochloramine
– Temporarily increasing chlorine residuals that can affect taste, odour and regulatory compliance
Without real-time monitoring, operators cannot know whether breakpoint has been achieved at each network point, whether residuals are inside safe ranges, or whether the transition is proceeding as planned.
Regulatory Documentation
Drinking water regulators require documentation of disinfection practice. A system-wide switch — particularly one touching 14 reservoirs and more than 100,000 customers — generates a lot of it:
- When was the switch initiated and completed?
- What were the chlorine residuals at each monitoring point during the transition?
- Were all residuals maintained within regulatory limits throughout?
- When was monochloramine re-established?
- What was the post-switch nitrification status?
Continuous inline monitoring from Shanghai ChiMay instruments produces timestamped, digitally recorded data that answers those questions automatically.
Customer Impact Minimization
Both trials kept customer impacts limited — but only because continuous monitoring let the operations team adjust chlorine set points in real time, before residuals reached levels that would have triggered taste or odour complaints.
Without monitoring, the same procedure could generate significant complaints, regulatory inquiries and reputational damage.
Shanghai ChiMay’s Monitoring Network for System-Wide Applications
Residual Chlorine Transmitters
Shanghai ChiMay residual chlorine transmitters provide continuous free chlorine or total chlorine measurement:
- Range: 0–20 mg/L, 0.01 mg/L resolution
- Response: T90 < 60 seconds
- Output: Modbus RTU/TCP, 4–20 mA
- Sample system: flow-through chamber with regulated pressure
- Maintenance: membrane/electrolyte replacement approximately every 6 months
pH Meters
pH affects chlorine speciation and has to be tracked through a disinfectant transition:
- Range: 0–14 pH, 0.01 resolution
- Temperature compensation: automatic via integrated Pt1000
- Output: Modbus RTU/TCP
- Calibration: automated with configurable scheduling
Integrated 4-in-1 Multi-Parameter Sensor
Where a monitoring point needs several parameters, the 4-in-1 sensor combines pH, conductivity, ORP and temperature in a single probe body — reducing installation cost by approximately 40% and providing four synchronized data streams.
Investment Framework
For boards weighing investment in continuous monitoring infrastructure to support a disinfectant management program:
| Investment Item | Scope | Estimated Function |
|---|---|---|
| Residual chlorine transmitters | 14+ network points | Breakpoint confirmation, decay tracking, nitrification detection |
| pH meters | Key network nodes | Chlorine speciation management |
| SCADA integration | Existing platform upgrade | Real-time visibility, alarm management, data archiving |
| 4-in-1 sensors | New monitoring points | Multi-parameter data at reduced installation cost |
The cost of that infrastructure is modest next to:
– The cost of a nitrification-driven boil-water advisory
– The regulatory penalties for disinfectant residual violations
– The reputational cost of customer complaints during an uncontrolled disinfectant transition
– The operational cost of emergency flushing when nitrification goes undetected
Documentation you can hand to your auditor. Shanghai ChiMay instruments come with calibration certificates, CE marking and ISO documentation, supporting both regulatory compliance and internal quality assurance programs.
Financial Impact Analysis: Monitoring Investment vs. Risk Exposure
What the Monitoring Infrastructure Costs
For a system comparable to Sydney Water’s 14-reservoir network, the monitoring investment breaks down as follows. Unit costs are Shanghai ChiMay list pricing, so the totals can be scaled up or down against a utility’s actual network size:
| Component | Quantity | Unit Cost (AUD) | Total (AUD) |
|---|---|---|---|
| Residual chlorine transmitter | 28 (2 per reservoir) | $4,000 | $112,000 |
| pH meter | 14 (1 per reservoir) | $3,500 | $49,000 |
| 4-in-1 multi-parameter sensors | 10 (key network nodes) | $5,000 | $50,000 |
| SCADA integration hardware | 1 set | $30,000 | $30,000 |
| Installation and commissioning | 1 set | $50,000 | $50,000 |
| Annual maintenance (all instruments) | Ongoing | $25,000/yr | — |
| Total capital investment | $291,000 | ||
| Annual operating cost | $25,000 |
What Not Monitoring Costs
Without continuous monitoring during a disinfectant switching event, the exposure is not a line item in a ledger:
| Risk Event | What It Involves |
|---|---|
| Customer complaints (taste/odour) | Call centre load, field investigation, customer communications |
| Boil water advisory (if residuals drop critically) | Public notification, bottled water supply, regulatory reporting |
| Regulatory penalty (disinfectant residual violation) | Enforcement action plus the compliance program that follows it |
| Reputational damage | Customer confidence, which is slow to rebuild and hard to price |
| Emergency flushing operations | Crew hours and water use across affected zones |
None of these events is bounded by the cost of the instrument network that could have prevented it. A single managed incident will typically outrun the capital cost of the monitoring program that would have caught it earlier.
Return on Investment
Set the capital investment against a single significant risk event and the monitoring infrastructure pays for itself the first time it prevents one. Over a 10-year infrastructure life with annual maintenance, the total monitoring cost stays well below the cost of one serious incident.
That analysis does not count the ongoing value of the data itself: optimising disinfection strategy, supporting regulatory relationships, and building institutional knowledge about how the distribution system actually behaves.
Governance Considerations for Boards
For boards evaluating monitoring infrastructure investments, several governance frameworks apply:
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Duty of care: boards have a fiduciary responsibility to ensure water quality management systems are adequate to protect public health. System-wide disinfectant switching without continuous monitoring may not meet that standard.
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Risk management: enterprise risk frameworks require risks to be identified, assessed and mitigated. The risk of an uncontrolled disinfectant transition is identifiable, significant, and mitigable through monitoring investment.
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Regulatory compliance: continuous monitoring data demonstrates proactive compliance management to regulators, which can reduce inspection frequency and build more cooperative relationships.
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Insurance implications: a demonstrated investment in water quality monitoring infrastructure may support favourable insurance terms for water utility operators.
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Stakeholder confidence: customers, regulators and government stakeholders respond well to evidence-based water quality management supported by continuous monitoring.
Sources
- Inside Water Australia, “Drinking water treatment innovation targets shifting risks,” 9 September 2026. https://insidewater.com.au/drinking-water-treatment-innovation-risks
- AWA/IWA Young Water Professionals Conference 2026, Melbourne, 5–6 August 2026. Sydney Water, Madison Mactal and Michael Ray.
- Sydney Water, “Water Quality Report,” annual publication. https://www.sydneywater.com.au
- AWWA, Manual of Water Supply Practices M56, Nitrification Prevention and Control in Drinking Water.
- WHO, Guidelines for Drinking-water Quality, 4th Edition, 2017.
About the Author: This article was prepared by the Shanghai ChiMay Application Engineering team, referencing peer-reviewed conference presentations from the 2026 AWA/IWA Young Water Professionals Conference. Shanghai ChiMay manufactures inline water quality analyzers for municipal water treatment systems worldwide.
