WATER SAFETY
100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%
100% 0% July August 6% September 0% October
100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%
100%
11% July August
3% September
0% October
Figure 1. Trend in L. pneumophila-positive outlets over the 3-month period at hospital based in London. Monochloramine introduced mid-July.
Figure 2. Trend in L. pneumophila-positive outlets over the 3-month period at hospital based in Surrey. Monochloramine introduced mid-June.
which are known to struggle to achieve good residuals at the extremities of systems, or within the hot water circuits, monochloramine residuals (>1.0ppm and up to 3.0ppm) were seen throughout, including in the hot water systems and at the furthest outlets, demonstrating its stability. Microbiological sampling was undertaken on a monthly
basis by a third party organisation, as a means to validate the efficacy of monochloramine treatment. Over 25 outlets at each hospital were identified as having had Legionella contamination prior to the introduction of monochloramine. Majority of positive outlets were fed by thermostatic mixing valves/taps. At the London site, during the previous 12 months prior to
monochloramine, on average 63 Legionella samples were taken monthly, and an average failure of 10 per month, or 18 per cent. Prior to the start of the study, 25 outlets were still positive with counts of Legionella ranging between 50 cfu/litre to 1300 cfu/litre. 19 of these outlets had counts of 100 cfu/litre or higher. At the Surrey site, during the previous 12 months prior to
Vikram Bamra
Vikram Bamra BEng is the Technical Services manager at Goodwater with over 17 years’ experience in the water treatment industry. His work primarily involves providing technical support, delivering specialist expertise, and driving product development and enhancement.
monochloramine, on average 71 Legionella samples were taken monthly, and an average failure of 9 per month, or 11%. Prior to the start of the study, 33 outlets were still positive with counts of Legionella ranging between 50 cfu/litre to 2850 cfu/litre. 23 of these outlets had counts of 100 cfu/litre or higher. Legionella samples were taken monthly over the three- month study, and each location had a pre-flush (sample collected immediately after outlet opened) and post- flush (outlet flushed for a minimum of 2 minutes before collection) sample collected at every visit. Microbiological analyses were performed by a
UKAS-accredited laboratory in accordance with BS EN ISO 11731, using BCYE (GVPC) agar with L-cysteine confirmation and serogrouping by latex agglutination.
Results and discussion Implementation of monochloramine dosing resulted in a substantial and rapid decrease in L. pneumophila detection across both sites. At the London site, the results were as follows:
n Following start-up of the Sanikill system, initial monochloramine residuals averaged at 1.25mg/L across outlets tested.
n Month 1: 50 samples taken in total (pre and post flush), no reported failures. The corresponding monochloramine residuals at these locations were at an average of 1.74mg/L.
n Month 2: 50 samples taken in total (pre and post 56 Health Estate Journal January 2026
flush). 3 positive counts reported (3%), ranging from 20 to 400cfu/litre. The corresponding monochloramine residuals at these locations were at an average of 1.24mg/L.
n Month 3: 48 samples taken in total (pre and post flush), no reported failures. The corresponding monochloramine residuals at these locations were at an average of 1.70mg/L.
All sampled locations were previously positive as discussed above, therefore demonstrating a complete reduction from 100% to 0% within four weeks, with full eradication remaining until month three. Monochloramine residuals were seen to gradually increase within the system as the disinfectant took control. At the Surrey site, the results were as follows:
n Following start-up of the Sanikill system, initial monochloramine residuals averaged at 1.35mg/L across outlets tested.
n Month 1: 54 samples taken in total (pre and post flush), 6 positive counts reported (11%), ranging from 20 to 3000cfu/litre. The corresponding monochloramine residuals at these locations were at an average of 1.45mg/L.
n Month 2: 58 samples taken in total (pre and post flush). 2 positive counts reported (3%), ranging from 80 to 200cfu/litre. The corresponding monochloramine residuals at these locations were at an average of 1.17mg/L.
n Month 3: 60 samples taken in total (pre and post flush), no reported failures. The corresponding monochloramine residuals at these locations were at an average of 1.94mg/L.
Monochloramine’s lower reactivity with organic matter compared to free chlorine allowed it to persist for longer within the distribution systems, maintaining effective residuals at distal outlets.
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