WATER HYGIENE AND SAFETY – SPECIAL REPORT
staff must be mitigated against by education and audit. Showers, taps, and other types of outlet, are extremely complex – an area expanded upon and discussed further in the overview of the handwash station.
n Contamination originating from drains is an area that has received attention in the last few years.11,14
been ignored, although Kohn in 1967 suggested this may be a major source of contamination.22
Viral (SARS) and
bacterial (CPE) outbreaks have been documented where drains have been identified as the source. Drains are now an area that need consideration and management by the Water Safety Group, and active research is ongoing.14,23
‘Ideal’ hot and cold water temperatures
Cold and hot water distribution systems present their own challenges in striving to control the growth of waterborne pathogens, as there will be a foreseeable risk where the water temperature is within the range of 20-45˚C. Below 20˚C organisms fail to multiply. In healthcare 55˚C is preferred as the lowest hot water temperature return, to provide an extra margin of safety in the control of waterborne pathogens.
Cold water system
To control the growth of microorganisms, Government guidance in the Water Supply (Water Fittings) Regulations recommends that cold water temperatures should not exceed 20˚C. The inlet, outlet, and surface water temperatures of cisterns and cold water feed/header tanks for the hot water calorifiers should not be greater than 2˚C above the incoming water supply at the property boundary, while at peripheral outlets, the water temperature should not be greater than 2˚C above the cistern and cold water header tanks within two minutes. Where there is a temperature gain, microbial proliferation and biofilm formation will occur. Among the main reasons why heat gain will occur in the cold water system are: n Failure to ensure sufficient turnover of the cold water.
n Poor design, where the cold water pipes have been placed above the hot water pipes.
n Positioning of the cold and hot pipes in the same service void.
n Lack of insulation of the cold water pipes.
n Association of cold water pipes with other heat sources, e.g. ceiling-mounted heaters.
Hot water services
Water temperature at the calorifier outlet is required to be at least 60˚C, with a minimum of 55˚C on flow and returns to
18 Health Estate Journal December 2020
Figure 5: A microbiologically fouled sieve of the type used to protect plumbing components.
all outlets and at the start of the hot water return, with a minimum return temperature to the calorifier at 50˚C. For outlets, hot water should be at 50˚C within 30 seconds, and 55˚C within one minute of that outlet being opened. There are a number of scenarios within a hot water system where microbial risks become apparent.
Calorifiers are water heaters and storage vessels. The incoming cold water enters at the base, below the heating coil, where the cold water mixes with the hot water and results in a lower temperature. The bottom of the calorifier is also where sediment collects, and this combination of sediment, which provides nutrients for the bacteria, and the lower temperature, will become a bacterial breeding ground. Anti-stratification or shunt pumps should thus be used to ensure mixing of the water, and the calorifier should be inspected and maintained to remove sediment. The greater the reduction of the hot water from 50˚C ,the greater the chances of microorganisms growing in the water. n Hot water pipes should be insulated to prevent heat loss.
n Hot water circulation pumps should be used to regulate the balance of the individual pipe branches and different loops, alternated with standby pumps, which may otherwise contain stagnated water that would encourage microbial growth.
n Expansion vessels are used to reduce pressure surges, but use bladders made from EPDM that will initiate and promote biofilm formation of waterborne pathogens.
n Keeping hot water circulating through all the various return loops simultaneously can be difficult to
achieve. Continuous monitoring of temperatures is aided by strategic placement of temperature monitoring probes linked to the building management system.
n The presence of inline strainers, used to protect the plumbing components, will also provide a breeding ground for the growth of Legionella and P. aeruginosa biofilms, and should be included in routine cleaning, maintenance, and disinfection procedures. (Figs 2 & 3).
Particular risks at the periphery The periphery of the system is particularly vulnerable to biofilm formation. If one arbitrarily defines the periphery as the last two metres of the pipework, then it is here where water becomes stationary unless the outlet is being used, and temperatures migrate to the ambient ideal for bacterial growth. Additionally, the periphery requires materials to be employed, even though WRAS-approved, that have a naturally higher propensity to biofilm formation. A further factor is retrograde contamination, which can be introduced by, for example, poor cleaning practices. While it should be possible to keep the main body of water free of significant bacterial contamination (with systemic contamination, outbreaks may occur), it is nigh impossible to keep the periphery clear of microbial contamination. In well- managed systems, positive water sample cultures usually reflect contamination of the periphery of the system, confirmed by high pre-flush, and low or absent post-flush, counts.
Outlets ‘predisposed’ to colonisation Outlets are predisposed to microbial colonisation for a number of reasons – including a series of complicated
The drain has often
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