Solving Water Age Problems
with AMI & Water Quality Sensors
The City of Gainesville, Georgia integrated Halogen MP5-A sensors with Sensus FlexNet AMI infrastructure to enable demand-based automatic flushing at remote dead-end locations. The sensor ran continuously for 6 months at 184 PSI with 99.875% uptime — no maintenance, no calibration, no service visits.
This paper documents the integration architecture, installation approach, data flows, and operational results — providing a replicable model for utilities looking to move from time-based to condition-based flushing.
Trial Results — Gainesville, Georgia
The Water Age Problem
Water quality degrades as it travels through distribution systems. The time between when water leaves the treatment plant and when it reaches a customer — known as water age — is directly correlated with declining disinfectant residuals. Even well-designed systems have water age problems, especially at dead ends where consumption is too low to maintain turnover.
Gainesville services rural areas many miles from its treatment plant. In dead-end sections, water age was causing chlorine and pH levels to drift outside acceptable ranges — resulting in taste and odor complaints and requiring periodic flushing to restore water quality.
The Problem with Manual Flushing
Without automated flushing, crews had to be dispatched to manually open valves or hydrants. This creates inconsistency due to workload variations, traffic, weather, and available labor. Each flush can require up to 140,000 gallons depending on the location — and without water quality data triggering the flush, crews often over-flush or miss the optimal timing window.
How Gainesville Built Remote Flushing
Gainesville established remote flushing sites using Sensus ally water meters with integrated remote shutoff valves. For higher-flow sites, a novel automated system was developed using a Sensus 2" Omni meter attached to a ClaVal on/off valve. This gives the city remote control over flushes plus a precise record of flushing volume for non-revenue water tracking.
Remote Control
Flushing sites controlled remotely via Sensus FlexNet AMI. No truck roll needed to initiate or stop a flush.
Off-Peak Scheduling
Flushes conducted at lower rates for longer durations during off-peak hours — evenings and nights — reducing impact on system pressure.
Volume Tracking
Sensus metering provides a precise record of flushing volume, enabling accurate non-revenue water accounting and optimization over time.
Why Gainesville Chose the Halogen MP5-A
In a previous demand-based flushing trial, Gainesville used an online DPD instrument for remote chlorine monitoring but found it insufficient. pH rose to unacceptable levels in colder months. Maintenance was required every 45 days. The instrument could not handle freezing temperatures. Gainesville needed something better.
Measures Both Chlorine & pH
Previous equipment could only measure chlorine. Gainesville found pH rises to unacceptable levels in colder months — making dual monitoring essential for reliable trigger logic.
No Maintenance for 6+ Months
The MP5-A required no maintenance or calibration for at least six months — compared to the previous DPD instrument that required service every 45 days.
Direct Wet-Tap Installation
Installed by wet-tapping directly into active distribution mains. Operates in freezing temperatures without needing service — a key requirement for outdoor vault installations.
Battery Operation
Eliminates the need for utility power at remote flushing sites. Low-power mode enables up to 6 months of operation on a 50 AH battery charge.
Zero Waste Stream
No sample line or drain required. Minimizes non-revenue water versus instruments that require up to 140,000 gallons per year in waste stream discharge.
Sufficient Resolution for Trigger Logic
Provides enough resolution to reliably trigger flushing when chlorine drops to 0.35 ppm or when pH rises to 8.9 — the thresholds defined by Gainesville operators.
Integration Architecture
The Halogen MP5-A interface supports low-power mode for up to six months of battery operation on a 50 AH charge. Four 4-20 mA outputs connect to Sensus Smart Gateways for data transmission to the Xylem Data Lake Dashboard. Data uploads are triggered by the Smart Gateway every 15 minutes.
Wet-Tap Installation
A vault installation was used at the trial site due to pipeline depth and size. Sensor installation uses conventional wet-tapping equipment on an active pipeline — no shutdown required.
- check_circleCorporation stop valve installed first
- check_circleHalogen sensor assembly inserted into flow
- check_circleSample port enables calibration checks with handheld colorimeter
- check_circleIntegrated remover assembly allows sensor service without shutting the main
Gen 2 Sensor Interface
Based on trial feedback, Halogen introduced a next-generation interface with several improvements:
- check_circleBluetooth Mobile App for on-site calibration checks
- check_circleIP68 battery enclosure for batteries up to 100 AH
- check_circleSolar panel connection included
- check_circleTwo independent Smart Gateway triggers for reliable 4-parameter transmission
What the Data Showed
Chlorine Drops with Water Age, Recovers After Flushing
Data from the Xylem Data Lake clearly showed chlorine levels declining as water aged in the dead-end section, then recovering immediately after each flush event. The pattern was consistent and unambiguous — validating that the sensor resolution was sufficient to detect the conditions that should trigger flushing.
pH Rises Especially in Cold Months
pH gradually rose with water age and fell after flushing. The effect was significantly more pronounced during colder months — confirming that pH monitoring was essential to the trigger logic and validating the decision to require dual-parameter monitoring before moving to demand-based flushing.
Sensor Tracked Well with Lab Samples
Halogen reported values were compared against lab samples collected on-site with calibrated instruments. The sensor tracked well after a calibration performed in September 2024 — which was the first calibration since installation. The preceding deviation illustrates the importance of initial calibration alignment, while the subsequent accuracy confirms long-term stability.
Conclusion
The City of Gainesville is satisfied with the results and plans to deploy more sensors. The combination of Halogen MP5-A sensors and Sensus FlexNet AMI provides a practical, scalable path to demand-based flushing — replacing timed flushes with condition-triggered events that use less water, require fewer truck rolls, and provide documented water quality data.
A new sensor version measuring both free chlorine and monochloramine has since been released for municipalities that use monochloramine as their secondary disinfectant — extending the same approach to chloraminating systems.