AT-19-C042 -- Legionella Regulation, Cooling Tower Positivity and Water Quality in the Quebec Context

The implementation of new regulations concerning the operations of cooling towers and other evaporative cooling systems in the Canadian Province of Quebec prompted the mass collection of Legionella culture results. In order to test which factors of a water treatment program are most significant in controlling Legionella growth, the Legionella culture results were amalgamated with water quality results for over 300 cooling towers for an observation period greater than three years in duration. The study concludes that this regulation, including the sampling requirement led to a sharp decrease in the presence and level of the Legionella bacteria in the cooling systems studied. Current levels of Legionella detected, and current water temperatures are significant, causal factors in explaining Legionella positivity over many future periods of time, while chlorine levels and dispersant application rates are significant, causal factors in predicting Legionella levels 90 to 120 days in the future.