Building in legionella prevention

Guardian Water Treatment, legionella, maintenance, refurbishment
The hazards of short cuts — Steven Booth.

Legionella prevention and general water hygiene must be considered at a building's conception, with current trends often not meeting the reality of controlling unwanted pathogens. Steven Booth of Guardian Water Treatment looks at how to build-in legionella prevention from the outset.

All commercial buildings have water systems — used for heating, cooling and drinking. Leisure facilities such as swimming pools and spas have even more water, which potentially poses a risk to human health. For closed-circuit heating systems, bacterial contamination can seriously affect the efficient operation of the system.

Keeping water clean and free of pathogens must be considered at the design stage. Legionnaires’ Disease is well documented, but other bacteria, such as Pseudomonas can also cause illness as well as fouling and corrosion. While there are standards in place to prevent bacterial contamination, in our view they don’t always go far enough, with water hygiene an afterthought, rather than a serious design consideration.

As long as a building is considered ‘safe’ at hand over, this is often good enough for contractors and specifiers. However, down the line we see problems arising that could have been prevented or minimised should more thorough hygiene control measures have been put in place from the outset. Cutting corners in construction can be a false economy that more than makes up for itself in elevated maintenance costs.

Traditional water-softening techniques ensure that lime-scale formation is controlled throughout the entire system.

‘Value engineering’ is a key culprit here, with cost-effective ‘fit-and-forget’ water-treatment solutions such as magnetic water conditioners often favoured due their low-energy and low-maintenance credentials. Problems usually present themselves several months or years after commissioning, due to the fact that limescale formation is not controlled throughout the entire water system as effectively as with traditional salt-based water softeners.

We see many examples of supplementary treatment devices that end up failing or being turned off all together due to a lack of understanding in terms of their required planned-preventative-maintenance (PPM) regimes or their importance; training is key for all members of the building services and facilities management team.

In hot- and cold-water systems, the risk areas that support the growth of harmful bacteria are controllable with good design, followed by ongoing operation and maintenance. For example, dead legs and capped pipes should be avoided where possible, to prevent stagnation. If unavoidable, they must be flushed out regularly. Lower-use water outlets should be installed upstream of frequently used ones — for example, a seldom-used shower installed upstream of a frequently used toilet.

Some key trends in modern water-system design are likely to promote bacterial growth. Water saving for example, while great for environment, presents additional hygiene risks. Low-flow taps allow water to stagnate, creating the right conditions for legionella to grow. Rather than do away with water saving, by being aware of this, ongoing water system maintenance and treatment is even more important. Regularly running water through is important, a particular consideration where tenanted properties may lie empty for weeks at a time.

It also appears to be the norm for almost every tap in a modern building to be fitted with a thermostatic mixing valve (TMV); this practice doesn’t match with the HSE guidance on legionella control, and in some case increases the risks of bacterial proliferation.

We recommend a bespoke approach to water treatment, with legionella prevention based around a specific system and how it is used – for example automated dosing based on actual water conditions, rather than just throwing in chemicals, regardless of the necessity.

The common practice of fitting taps with TMVs (thermostatic mixing valves) doesn’t match with HSE guidance on legionella control.

There are non-chemical alternatives to water treatment that greatly reduce bacterial levels, without the use of biocides,. Two examples are photo-catalytic water purifiers that harness a specific frequency of light and photo-catalytic surfaces to create free radicals that break down harmful micro-organisms and other pollutants in water. Where chemicals are required, by tailoring dosing to a specific system and its usage, excesses in use can be avoided.

A non-chemical approach can work particularly well in closed-circuit water systems. The traditional filling and pressure testing of closed systems with biocide-treated water during construction has a number of problems. These include operatives coming into contact with chemicals and the low levels of biocide (so as not to pose too much risk to human health) resulting in not all bacteria being killed. Air testing, which is sometimes used as an alternative, also comes with its own health-and-safety issues.

By cutting the need for chemicals, health-and-safety risks are reduced, as well as improving a system’s sustainability credentials. Apart from potentially being harmful to the environment, biocides themselves can also cause corrosion; bromine, often used in cooling towers, is one such example. By cutting down their usage, equipment longevity can also be improved.

Regardless of how well a water system is designed and installed, ongoing maintenance is still essential. To make this as easy as possible, all parts of the system must be easy to access, with isolation valves included to facilitate maintenance and implement control measures. Remote monitoring will allow water treatment to be based on the real scenario, rather than a ‘one-size-fits-all’ approach that can lead to over-use of chemicals. As with many things in life, short cuts can often make things more difficult and expensive in the long run.

Steven Booth is associate director at Guardian Water Treatment.

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