Background: A cluster of sternal surgical site infections caused by Pseudomonas aeruginosa led to sampling of shower heads in patient rooms. Multiple subtypes of Pseudomonas aeruginosa were found and were genetically diverse from the patient isolates. Visible biofilm was found in showerheads in the cardiothoracic ward. Ways of minimizing formation and persistence of biofilm in the shower heads were sought. Methods: A low-dose chlorination dosing system was introduced in September 2018 to the circulating warm-water system supplying the building block where the cardiac surgery ward is situated. Of the 145 showers in that block, 70 shower heads were sampled and the shower heads were replaced. Of these, 35 were sampled at 3 months and 35 were tested at 6 months (biofilm prevention group). Of the remaining 70 shower heads, 35 were tested at 3 months and 35 at 6 months (biofilm removal group). Heterotrophic colony count (HCC) in CFU/mL was chosen as the outcome measure. Analysis was conducted in accordance with AS 4276.3.2 (2003). The microbial growth data followed a log-normal distribution due to the exponential growth of bacteria. The natural log of the data was therefore calculated, and results from each period were compared using analysis of variance (ANOVA). Free chlorine residual levels were controlled using a combination of feed-forward and oxidation reduction potential (ORP) feedback control, and levels were retested and adjusted during the review period using N,N-diethyl-p-phenylenediamine (DPD) chemistry. Results: Mean and median levels of log HCC data are shown in Fig. 1. We detected a statistically significant difference in HCC between the 6-month-old untreated shower heads (group B) and treated shower heads (Group D) (P < .001). Hypochlorite was generally dosed at a concentration of 0.5 mg/L free chlorine for the first 3 months, and 1.5 mg/L for the second 3 months. Approximately 65% of the chlorine was lost as it travelled around the system. Discussion: Waterborne pathogens, especially multiresistant Gram-negative bacilli, have been increasingly recognized as hospital-acquired pathogens. Many instances of the transmission of these pathogens have been reported, from premise plumbing to patients, and have been confirmed using molecular typing techniques. Conclusions: A low-dose chlorination system of the circulating warm-water supply seemed effective in preventing biofilm formation and reducing existing biofilm in shower heads using HCCs as a measure of biofilm. This information adds to the potential armamentarium for controlling the spread of these waterborne pathogens.