The Ultimate Water Hygiene & Legionella Control Glossary
Search Our Glossary
- 01
The Approved Code of Practice (ACoP) L8 is UK guidance from the Health and Safety Executive (HSE) on controlling Legionella bacteria in water systems. It outlines legal responsibilities, risk assessments, and control measures to prevent Legionnaires’ disease, ensuring safe water management in commercial and residential buildings.
- 02
The process where bacteria, such as Legionella, spread through tiny water droplets suspended in the air, increasing infection risk in poorly maintained water systems.
- 03
A physical space between a water outlet and the highest possible water level in a system, preventing backflow and contamination of potable water supplies.
Learn more at our Backflow Prevention page.
- 04
The natural temperature of standing water within a system, which influences bacterial growth rates. Water temperatures between 20–45°C create an ideal environment for Legionella bacteria to multiply.
- 05
A safety device installed in taps and showers to prevent dangerously high water temperatures that can cause burns. A typical example is a thermostatic mixing valve, or 'TMV' for short.
Learn more about TMV's at our blog: TMV Servicing
- 06
A device that automatically flushes water outlets at set intervals to prevent stagnation. This reduces biofilm formation and minimises the risk of Legionella growth in low-use water systems.
- 07
The average volume of water used daily in a system, helping to assess consumption patterns and ensure adequate supply. Understanding ADD assists in system design and maintenance.
- 08
A divider installed inside a water tank to control the flow of water, ensuring proper circulation and preventing stagnation, which reduces the risk of bacterial growth.
- 09
The unintended reverse flow of water, which can lead to contamination by allowing non-potable water to enter clean water supplies. Backflow prevention devices are essential in maintaining safe drinking water.
Read more in our Backflow Prevention pages.
- 10
A mechanical device used to prevent contaminated water from reversing into clean supply lines, such as a Reduced Pressure Zone valve (RPZ) or Double Check Valve (DCV). These devices are critical in water systems to maintain hygiene and compliance with regulations.
Learn more in our Backflow Prevention page.
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The routine testing of water samples to check for bacterial contamination, ensuring compliance with water safety regulations.
- 12
A mechanical device that regulates water flow into tanks or cisterns. It operates with a floating ball that opens and closes the valve, ensuring water levels remain controlled.
Read our blog on the different types of ball valves available: Choosing the Right Ball Valve.
- 13
A thin, slimy layer of bacteria and organic matter that adheres to surfaces in water systems. Biofilms provide an environment where harmful bacteria, including Legionella, can multiply.
- 14
A valve used to remove sediment and impurities from water systems, especially in boilers and hot water cylinders, to maintain efficiency and prevent bacterial growth.
- 15
A pump designed to increase water pressure in systems with inadequate supply. It ensures adequate water distribution in high-rise buildings and commercial facilities.
See one of our recent projects in which we installed a new booster pump set: Mains Conversion & Booster Set.
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Water extracted from underground aquifers via a borehole. It may require treatment to ensure it is free from bacteria and contaminants before use.
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A water heater that indirectly heats water through a coil or heat exchanger. Legionella bacteria can thrive in calorifiers if temperatures are not properly maintained.
See our Hot Water Services pages for more info.
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The controlled addition of chemicals such as disinfectants, corrosion inhibitors, or pH stabilisers into water systems to maintain water quality.
- 19
A water disinfection process that uses chlorine to kill microbial activity within the water storage and distribution system.
- 20
The amount of chlorine remaining in treated water after initial disinfection, ensuring continued protection against bacteria.
- 21
A protective coating or liner inside a water storage cistern that prevents leaks and reduces the risk of contamination from corrosion or biofilm formation.
- 22
A tank that stores cold water before distribution. Proper maintenance and temperature control are crucial to prevent stagnation and Legionella growth. Visit our Cold Water Tanks page to read more.
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A chemical added to water systems to slow down or prevent rust and scale formation in pipes and tanks.
- 24
A common abbreviation for a cold water storage tank, which holds potable or non-potable water for distribution. Read more about our cold water tank services in our Recent Projects pages.
- 25
A section of pipe where water stagnates due to little or no flow. Dead legs increase the risk of bacterial growth, including Legionella. - Read more here.... Dead Leg Piping
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The process of mixing water layers in a tank or reservoir to ensure uniform temperature distribution. This prevents stagnant, cooler zones that can promote bacterial growth.
- 27
The process of using chemicals (such as chlorine) or heat to eliminate harmful microorganisms in water systems.
Learn more at our tank cleaning page.
- 28
A pump that precisely injects chemicals into a water system, often used for disinfection and corrosion control.
- 29
A pipe that delivers water from a storage tank to distribution points. Maintaining flow prevents stagnation and microbial growth.
- 30
The removal of limescale and mineral deposits from pipes, boilers, showers, water heaters and water tanks to improve efficiency and hygiene.
- 31
A valve used to empty water storage tanks and pipework for maintenance or cleaning.
