WATER SYSTEMS
Taste or odour problems Where taste or odour problems in drinking water exist, microbiological monitoring for TVCs may be necessary. However, routine microbiological monitoring for TVCs is not recommended, as there is no direct association with TVCs and waterborne pathogen presence. Samples must be taken from locations representative of the water source, treatment plant, storage facilities, distribution network, and delivery points. In selecting sampling points, each locality should be considered individually, but the following general criteria apply: n Sampling points should be selected so samples are representative of the different water sources.
Taps should be cleaned before the rest of the clinical washhand basin. Care should be taken to avoid transferring contamination from basin to basin.
control waterborne pathogens within domestic hot and cold water systems, we must fully understand the mains incoming water quality before establishing a suitable water management plan. Water temperature is just one aspect of water management. To spread through a water system of any size, Legionella requires both an optimum temperature range, i.e. between 20 and 45 °C, and available nutrients.
Suitable nutrients for Legionella The need for suitable nutrients is where hard water becomes a potential Legionella issue. Nutrients are typically present in the form of biofilm, and biofilms harbour microbes that Legionella bacteria can use as nutrients… and, of course, nutrients encourage bacteria growth. There are three elements necessary for biofilm to occur: 1 Moisture – this allows the bacteria to grow / spread.
2 Bacteria – either a single species or several.
3 A surface for the bacteria to adhere to. Biofilms will adhere to many surfaces –
from skin to metal and plastic, and act as a very effective ‘hideout’ for bacteria, which can be very difficult to remove. Effective hygiene, keeping the water moving to prevent stagnation and build-up of the necessary nutrients for bacterial growth, and keeping the cold water cold, and the hot water hot, are all key.
Water sampling techniques To confirm effective microbial control, sampling in both domestic and industrial water systems is essential. However, the importance of correct water sampling procedures is often overlooked. Before undertaking microbial sampling, one should have the correct information, understand the reason, note the time of sampling, and the extent of pipework to
34 Health Estate Journal February 2023
be sampled, know the type of analyses required, who will conduct the process, and the sample processing location – e.g. an ‘in-house’ or external laboratory. Appropriate sample storage facilities, and the timeframe for transporting the sample bottles are key, since some analysis requires the containers to be stored in a cool place for a set maximum period. Water collected for P. aeruginosa analysis, for example, should be processed within two hours, but if this is not possible, should be refrigerated within two hours, kept at 2-8 °C, and processed within 24 hours. Samples must also be kept apart from both hot and other cold samples to prevent temperature ‘cross-contamination’.
Need for sufficient training Personnel undertaking sampling should have sufficient training and information to perform the task correctly, and a general understanding of the bacteria’s characteristics, to appreciate the steps required to maintain the samples’ bacterial load until the laboratory receives them. The time between sample collection and analysis should generally not exceed six hours, with 24 hours considered the absolute maximum. All Mycobacterial analysis requires different storage and / or transport requirements. Samples for Legionella analysis can be stored at an ambient temperature, and should preferably be delivered to the lab within 24 hours, but after no more than 48, with Pseudomonas aeruginosa samples kept at between 2 and 8 °C, and processed within 24 hours. Sampling should identify the quality of the water (total viable counts of bacteria, or TVCs) both from the supply company, and at point of use. Any significant variation between the two has important implications for remedial action, as TVCs are a good indicator of general water quality.
n The sample points should include areas that yield samples representative of the conditions at the most unfavourable sources or places in the supply / distribution system – such as unprotected sources, loops, low-pressure zones, ends of the system, and high-risk water exposure areas for patients / the public.
n Sampling points should be uniformly distributed throughout a piped distribution system, with the number proportional to the number of links / branches.
n They should be located so that water can be easily sampled from reserve tanks (cold water tanks, RO units, calorifiers, and cooling towers etc.), and water components.
n In systems with more than one water source (mains water, borehole water supply), the sampling point location should factor in the area and number of inhabitants served by each source.
n There should be at least one sampling point directly after the clean water outlet from each treatment plant.
n Sampling points in the water distribution system may be classified as ‘fixed’, ‘random’, or ‘variable’.
Fixed samples Fixed samples are useful when results must be compared over time, but limit the possibility of identifying local problems. Sampling regimes using variable or random outlets are more likely to detect local problems, but less useful for analysing changes over time. Areas sampled should include hydrotherapy pools, augmented care and maternity wards, burns units, and areas housing the immunocompromised, elderly, and very young. When sampling water that may contain
even traces of chlorine or other biocide, the biocide must be inactivated, or microbes may be killed during transit, giving an erroneous result. The sample bottles should thus contain sodium thiosulfate to neutralise any chlorine, copper, and silver. Stringent hygiene is key throughout; this includes the box used to carry samples, which should be cleaned and disinfected after each use.
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