Introduction
Legionella is a bacterium that can cause pneumonia in its victims when they come into contact with a contaminated aerosol of water. It is a bacterium that multiplies in conditions where there is water stagnation or low flow, warm temperatures between 20-45°C, and a food source. All these conditions can occur when a water system is stagnant (no water movement). Water systems become stagnant for a number of reasons. These include buildings being mothballed, school holidays, and the period between system commissioning and hand over.
Mothballed Buildings
Buildings being mothballed is particularly prevalent at this time when huge number of buildings are being left unoccupied because of Covid-19. Office workers are now sat toiling in their kitchens rather than inhabiting their normal working environment.
School Holidays
School holidays are always a challenge for councils- caretakers are expected to replicate the water turnover in secondary schools by running taps throughout the building. This is a task that is often neglected due to more, seen to be, pressing jobs or the fact that the task is too large for one person to undertake.
Water System Commissioning
In practice the time between building water system commissioning and handover should be as short as possible but often this is not the case. Buildings often become contaminated with biofilm containing legionella during this phase. Biofilms which form before system handover become obdurate and sometimes impossible to remove. This can affect the performance of the water system in the long term.
Legionella Control: Flushing Guidance.
The main guidance in HSG 274 Part 2, Legionnaires’ disease Part 2: The control of legionella bacteria in hot and cold water systems is to flush a system when it is not in use. Flushing requires attempting to mimic the buildings water use whilst minimising water loss. Given that outlets should be flushed for 5 minutes after the temperature has stabilised this could use a lot of water. Flushing also takes up considerable labour and time.
Huwa-San Dosing
A more cost effective, and safer alternative to this would be to dose the water system with Huwa-San, silver stabilised hydrogen peroxide. The benefits that this would give the system are:
1) The system is protected against legionella, pseudomonas, and other microbiological growth.
2) The system would not develop a biofilm that could potentially create on-going problems
3) Costs would be reduced- There would be less water usage and labour costs
4) The flushing operators would be safer
Huwa-San can be used to ensure favourable water conditions when buildings are out of use. Because of very its unique stability the silver ion in Huwa-San reacts slowly with chloride in the tap water which means very little change in peroxide residual over long periods of time. This stability allows Huwa-San to remain effective against biofilm and bacteria in water systems for several weeks. Independent studies show that Huwa-San has a half-life of 5 weeks in town mains water. (The starting concentration will reduce to half in 5 weeks).
We have developed a procedure for treating buildings where the water is stagnant based on Huwa-San’s unique stability.
Procedure for Dosing Huwa-San to Stagnant Water Systems.
- Dose the tank or the mains fed water system to 800ppm Huwa-San/400ppm peroxide.
- Pull through to the furthest outlets then work backwards to your tank and/or calorifier. Ensure the Huwa-San is pulled through to all the outlets. This will provide the whole system with protection.
- Check the levels at the far points of the system. These should be 800ppm Huwa-San/400ppm peroxide. Additional dosing may be required but once 800ppm Huwa-San/400ppm peroxide is achieved no further water should be removed from the system. To achieve 800ppm Huwa-San/400ppm peroxide 800ml of Huwa-San TR-50 should be added per 1000 litres of water.
- After 21 days check the peroxide levels at the sentinel outlets of the system. The peroxide level may initially be zero due to the air water interface at the tap. However, after a couple of seconds good levels should once again be established.
- The sentinel outlets should be checked every 21 days after this point. Once the level of the Huwa-San falls to 200ppm Huwa-San/100ppm peroxide additional dosing should be carried out to re-establish 800ppm Huwa-San/400ppm peroxide in the system.
- When returning the system to use flush the Huwa-San level down to 200ppm Huwa-San/100ppm peroxide.
