A Multi-Parameter Source Water Risk Framework for Legionella Prediction in Ontario Cooling Tower Systems: Integrating Physicochemical Baseline Data, Adverse Water Quality Incident Records, and Provincial Outbreak Surveillance 2019–2025
Description
This study presents a multi-parameter source water risk framework for Legionella prediction in Ontario cooling tower systems, integrating three independent provincial datasets: 60 years of Ontario Provincial Water Quality Monitoring Network (PWQMN) data comprising 7,630,482 measurements across 2,128 monitoring stations; Ontario Drinking Water System Adverse Water Quality Incident (AWQI) records from 2020 to 2025 covering 18,114 documented incidents; and Public Health Ontario legionellosis surveillance data from 2019 to 2025 documenting 354 confirmed cases annually with a 76.6% hospitalization rate.
Analysis reveals that the Grand River watershed scores 14 of 15 on a composite Legionella risk index derived from peer-reviewed physicochemical risk parameters. Simultaneous seasonal elevation of hardness (mean 278 mg/L), temperature (Q3 mean 20.8°C, within the amoeba growth window), turbidity (mean 42.7 NTU), total phosphorus (above Ontario eutrophication threshold), and iron (311 µg/L) creates a predictable multi-parameter convergence every summer that current Water Management Plans do not address.
Five years of AWQI records reveal that low chlorine residual incidents — a documented consequence of elevated hardness and pH reducing disinfection efficacy — increased from 142 in 2021-22 to 192 in 2024-25, following a parallel trajectory to Legionella case counts. The 2024-25 fiscal year recorded a 10-fold increase in documented exceedances coinciding with the largest Legionella outbreak in Middlesex-London Health Unit history.
The Presignal Multi-Parameter Legionella Risk Framework is proposed for integration with ASHRAE Standard 188-2021 Water Management Plans. Ontario currently has no provincial cooling tower registry and no mandatory predictive monitoring standard. This paper provides the scientific basis for both.
Related work: Grand River Source Water Paper — DOI: 10.5281/zenodo.19653415. Legionella Seasonal Correlation Paper — DOI: 10.5281/zenodo.19695022.
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Additional details
Related works
- Is documented by
- Software: https://www.ufosworldwide.com/aquasignal/ (URL)
- Is supplement to
- Preprint: 10.5281/zenodo.19653415 (DOI)
- Preprint: 10.5281/zenodo.19695022 (DOI)
- Preprint: 10.31223/X5J47D (DOI)
References
- Almonacid Garrido, M.C., García-Alonso, A., Villanueva-Suárez, M.J., & Tenorio-Sanz, M.D. (2026). Microbiological and physicochemical parameters related to Legionella spp. colonisation in hot water distribution systems in Madrid. Applied Sciences, 16, 1628. https://doi.org/10.3390/app16031628
- ASHRAE. (2021). ANSI/ASHRAE Standard 188-2021: Legionellosis risk management for building water systems.
- Carter, J. (2026). Chronic source water quality exceedances in the Grand River watershed. Zenodo. https://doi.org/10.5281/zenodo.19653415
- Carter, J. (2026). Seasonal source water temperature as a predictive indicator for Legionella outbreak risk in Ontario healthcare facilities. Zenodo. https://doi.org/10.5281/zenodo.19695022
- Kerry, M.R. (2024). Monitoring and detecting Legionella within evaporative cooling towers [PhD thesis]. University of Sheffield.
- Ontario Agency for Health Protection and Promotion. (2025). Legionellosis in Ontario 2024. Toronto: King's Printer for Ontario.
- Ontario Agency for Health Protection and Promotion. (2025). Surveillance report: Legionellosis in Ontario January 1 to December 3 2025. Toronto: King's Printer for Ontario.
- Ontario Ministry of the Environment, Conservation and Parks. (2024). Provincial Water Quality Monitoring Network. DataStream. https://doi.org/10.25976/tnw0-3x43
- Rebellato, S., Lee, C., Gardner, C., et al. (2023). Community Legionella outbreak linked to a cooling tower, 2022. Canada Communicable Disease Report, 49(9), 380–388.
- Harrison, K., Proctor, C.R., Martin, A., Williams, K., Pruden, A., & Edwards, M.A. (2020). Chlorine disinfection of Legionella spp. and Acanthamoeba under warm water premise plumbing conditions. Microorganisms, 8, 1452.