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Managing Water Safety

Excerpt from Water Safety article that appeared in the December 2017 issue of The Pulse magazine (member magazine of the Hospital Estates and Facilities Management Association or HEFMA).  Read the full text below or, adjacent, open a pdf of the article as it appeared in the magazine.

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Essential for life, water can also be responsible for deaths if it is not managed properly to ensure it is safe and not distributing bacteria around the building and to vulnerable patients. Pulse finds out about some of the latest technology for maintaining water safety, monitoring water temperature and testing for bugs.

Earlier this year, HTM 04-01, the guidance for safe water in healthcare premises, was updated to make it easier for sites to test thermostatic mixing valves (TMVs).  Essentially, however, the advice around maintaining water safety across the hospital has not changed.

Horne Engineering supports the industry’s traditional thermal regime as the recommended method of pathogen control for waterborne organisms. Keep hot water hot (above 60°C); cold water cold (below 20°C); ensure good cold water turnover and minimise system deadlegs – especially dead-ends - that cool to the ambient temperature, which is favourable for bacteria proliferation.

 

Managing water in old buildings

‘One of the problems with old systems is that they were designed for a specific demand of warm and cold water, and it is likely that, with recent efforts to conserve water, greatly reduced flow rates will have been retrospectively applied to such systems.  The result?  Reduced turn over and flow rate encourages greater development of biofilm on the internal pipe walls’, says Hannah Berry, Marketing Manager of Horne Engineering. 

Hans Curt-Flemming, a German scientist specialising in the study of biofilm, has determined that 95% of the biomass load in water systems resides on the walls of the system and only 5% is planktonic, or carried in the water flow.  If left unchecked, the wall biofilm will grow and periodically disperse downstream as bits break off into the passing stream, thus contaminating other parts of the system.

Horne has always been an advocate of high velocity flushing – this means flushing the system to drain from an integral drain point just upstream of Horne TMVs, showers and the Optitherm tap.  ‘This is generally recommended practice during the commissioning of new installations; for removal of any pipework debris, swarf and other construction contaminants, but we also recommend periodic flushing, at higher velocity, to remove excess biofilm to drain.  The changed velocity increases shear forces at the liquid-solid boundary, mechanically scouring the biofilm off the wall and into the flow...and to drain’. 

Reduced flow rates also increase the build-up of biofilm within the basin trap as there is not enough pressure behind the flow to sufficiently clear the fouling.  This can exacerbate the situation, as the trap is a well-identified source of contamination for retrograde colonisation of the water system via the tap terminal fitting.

 

Retrograde contamination

An increasing problem today is posed by pathogens that enter the hospital water system from the ward environment. Pseudomonas Aeruginosa, for instance, predominantly inhabits the last two meters of pipework before the tap terminal fitting/outlet.  ‘Isolates from the water system typed as being resistant to a specific antibiotic or, increasingly, as being multi-drug resistant (MDR), can only have arrived there as a result of retrograde contamination (RC), explains Berry.

There are a number of causes of RC, including splashing during hand washing, poor cleaning practices or misuse of the (dedicated) hand-washing facilities.  The outcome is that the water system - the part proximal to the outlet fitting - becomes a reservoir of potential further infection.  Unmanaged, that contamination can extend up the cold pipework to other parts of the system.

The outlet fitting on the tap also has a crucial part to play with respect to reducing contamination.  ‘It is inherently vulnerable - not because of its structure or composition - but because it is situated at and serves as the interface between two phases: the non-sterile air of the ward environment and the hospital water system.  It will inevitably be subject to contamination as well as evaporation.  Therefore, the interface itself, the surface area of that phase boundary, needs to be an optimal size.

In the case of Horne’s Optitherm thermostatic tap, the phase interface is reduced to the diameter of the outlet’s flow conditioner (which is also designed specifically to reduce splashing).  Its design intentionally exploits the water’s natural surface tension and stops the spout draining down.  ‘This is important: all a drain-down spout can do is intake air - to replace the displaced water - that is invariably contaminated, and significantly increase the surface area of the air/water phase boundary.  Throw in the agreeable temperature and the moist darkness and, hey!  It’s party time!

 

In-line thermal disinfection

A hospital is a complex environment and it is almost inevitable that at some point in its operational lifetime, any tap or shower fitting will be identified as a reservoir of infection for a particular pathogen.  Pseudomonas Aeruginosa might be grabbing the headlines, but the water system could feasibly become contaminated with just about any hydrophilic pathogen that is present in the ward environment.  Recognising this and putting processes in place to manage RC is all that is required.

Hannah Berry outlines the benefits of in-line thermal disinfection.

‘The Horne ILTDU (in-line thermal disinfection unit) cannot prevent RC but it does allow for it to be effectively managed.  The ILTDU facilitates straightforward thermal disinfection utilising the locally available hot water supply; and does so from a point that is some distance from the outlet, thus covering the more susceptible cold water pipe drop.  Everything downstream: the cold water pipe drop, strainers, check-valves, TMV, all the way to, and beyond, the outlet fitting can be routinely raised to system temperature and disinfected.

‘Horne recommend routine disinfection using the ILTDU at a temperature no less than 60°C for a minimum of 10 minutes.  To conserve hot water the flow rate can be throttled back slightly, but full immersion of the outlet fitting or the shower spray pattern must be achieved for the full 10 minutes.  Tests at participating hospitals have shown that when this advice is followed the ILTDU is capable of resetting P. Aeruginosacounts to zero.

ILTDU thermal disinfection should be paired with high velocity flushing to remove excess biofilm and optimise the quality of water entering and exiting the tap or shower fitting.

‘This combination of HV flushing and thermal disinfection is the only truly workable solution for minimising the risk of the water supply becoming a reservoir of infection and, with the growing global threat of MDR bacteria, reducing reservoirs of infection will become increasingly important.

‘According to HTM 04-01, when a water outlet is identified as being contaminated, point-of use filters are allowed as a temporary protective measure until an engineering solution can be implemented.  Where no workable solution exists, HTM 04-01 Part B, Page 44, Paragraph 7.45 states continuous long-term use of POU filters is not recommended, except where there is no effective alternative.

‘There is now, however, a completely workable and significantly more cost-effective solution in the patented ILTDU.  There are some obvious limitations with POU filters: they are only effective for a finite period, generally 30 days, and changeover for new is required.  This can represent a significant and ongoing cost burden to a resource-limited NHS.  Not only that, the filter is just as susceptible to retrograde contamination and biofilm formation on its outer surfaces as the original outlet fitting.  Meanwhile it allows planktonic and waterborne pathogens to congregate on the upstream side of the filter, form a biofilm and proliferate under likely perfect conditions (favourable temperature, good oxygen supply and, perhaps, nutrient-rich fresh water flowing through it).  This may actually exacerbate the contamination of the system.

‘ILTDU’s compare favourably from a cost point of view.  Taking the cheapest POU filter as around £30 – so looking at the worst-case comparison – a single ILTDU with its operation key (the number of keys required should match the number of operatives and not the number of ILTDUs installed) will pay for itself in just over 5 and a half months.  Scale this up and the savings are substantial.  With an ILTDU there are no further costs, other than the labour for its routine operation.

There are additional savings to be had though: once the product and method are proven - by a number of water sample tests, over a series of weeks or months, showing PA reset to zero – then the frequency of water testing can also be reduced.