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A suspension in a gaseous medium of solid particles, liquid particles or solid and liquid particles having negligible falling velocity.
(singular bacterium) a microscopic, unicellular (or more rarely multicellular) organism.
A substance which kills micro-organisms.
A community of bacteria and other micro-organisms, embedded in a protective layer with entrained debris, attached to a surface.
Water discharged from the system to control the concentration of salts or other impurities in the circulating water; usually expressed as a percentage of recirculating water flow.
An apparatus used for the transfer of heat to water in a vessel by indirect means, the source of heat being contained within a pipe or coil immersed in the water.
A chemical used for microbiological control.
Installation of plant, pipes and fitting in which cold water is stored, distributed and subsequently discharged.
An apparatus through which warm water is discharged against an air stream; in doing so part of the water is evaporated to saturate the air and this cools the water. The cooler water is usually pumped to a heat exchanger to be reheated and recycled through the tower.
A length of pipe closed at one end through which no water passes.
Pipes leading to a fitting through which water only passes when there is draw-off from the fitting.
A clip slide is a means of testing the microbial content of liquids. It consists of a plastic carrier bearing a sterile culture medium which can be dipped in the liquid to be sampled. It is then incubated to allow microbial growth. The resulting microbial colonies are estimated by reference to a chart.
A process which destroys or irreversibly inactivates micro-organisms and reduces their number to a non-hazardous level.
Pipework which distributes water from hot or cold water plant to one or more fittings/appliances.
Hot and cold water intended for personal hygiene, culinary, drinking water or other domestic purposes.
Organic growth or other deposits on heat transfer surfaces causing loss in efficiency.
Installation of plant, pipes and fittings in which water is heated, distributed and subsequently discharged (not including cold water feed tank or cistern).
A form of pneumonia caused by Legionella bacteria.
Type of aerobic bacterium which is found predominantly in warm water environments. (Singular of legionellae).
One of the causative organisms of Legionnaires’ disease.
Any illness caused by exposure to legionella.
A disease caused by species of Legionella, an upper respiratory illness less severe than Legionnaires’ disease.
Water which is added to a cooling water system to compensate for wastage (e.g. via system leaks), evaporative loss and bleed.
An organism of microscopic size including bacteria, fungi and viruses.
A non-oxidising biocide is one that functions by mechanisms other than oxidation, including interference with cell metabolism and structure.
A food source for micro-organisms.
Agents capable of oxidising organic matter, e.g. cell material, enzymes or proteins which are associated with microbiological populations resulting in death of micro-organism, the most commonly used oxidising biocides are based on chlorine or bromine (halogens) which liberate hypochlorous or hypobromous acids on hydrolysis in water. The exception is chlorine dioxide, a gas which does not hydrolyse but which functions in the same way.
Heat treatment to destroy micro-organism usually at high temperature.
Parts per million: a measure of dissolved substances given as the number of parts there are in a million parts of solvent. It is numerically equivalent to milligrams per litre mg/l with respect to water.
Indentifying and assessing the risk from Legionellosis from work activities and water sources on premises and determining any necessary precautionary measures.
Chemicals used to control scale. They function by holding up the precipitation process and/or distorting the crystal shape, thus preventing the build-up of a hard adherent scale.
A sub-group of the main species.
For a hot water services – the first and last taps on a recirculating system. For cold water systems (or non-recirculating hot water systems), the nearest and furthest taps from the storage tank. The choice of sentinel taps may also include other taps which are considered to represent a particular risk.
Aquatic micro-organisms adhering to a surface normally as part of a biofilm.
A general term for soft mud-like deposits found on heat transfer surfaces or other important section of a cooling system. Also found at the base of calorifiers and cold water storage tanks.
A circulation pump fitted to hot water service/plant to overcome the temperature stratification of the stored water.
A mucus-like exudates which covers a surface produced by some micro-organisms.
The condition where water ceases to flow and is therefore liable to microbiological growth.
Heat treatment to disinfect a system.
Mixing valve in which the temperature at the outlet is pre-selected and controlled automatically by the valve.
The total number of culturable bacteria (per volume or area) in a given sample (does not include Legionella).