The advice offered in this section has been drawn up in the spirit of general guidance. If there is any doubt, in any case, expert advice must be sought.

What regime should be used when monitoring water quality in water tanks?

Answer

There are two sets of requirements for monitoring water in water tanks, those required for the control of legionella (set out in Legionnaires’ disease- The control of legionella bacteria in water systems a combined Health and Safety Commission approved code of practice and guidance from the Health and Safety Executive) and those for maintaining drinking water quality (set out in British Standard 6700:1997 and enforceable under The Water Supply (Water Fittings) Regulations 1999). The legionella control regime advocates

• the water should be kept cooler than 20°C
• the temperature at the supply (float valve, for example) and farthest accessible point within the tank should be checked twice a year (in winter and summer)
• the tank be inspected at least once each year for integrity (particularly against the ingress of foreign material via covers, access hatches, overflow pipes and overflow warning pipes) and cleanliness (excessive scale or corrosion, excessive accumulation of sediment, foreign bodies, slime growth)
• the water consumption should also be checked once a year to confirm that the tank is of a suitable size to avoid stagnation: this can easily be done by closing off the supply and monitoring the reduction in water level over the course of a typical day (the capacity should be approximately equivalent to one day’s consumption).
  
  The drinking water quality regime requires

• the water should be kept cool (good practice would be to limit any temperature rise to 2°C above the supply temperature)
• the water should be sampled and tested twice each year (e.g for total bacteria levels (TVC) at 22°C and 37°C, coliforms and E. coli).

Acceptable levels of total bacteria are not specified beyond an implicit requirement that they should not be significantly higher than the corresponding figures in the supply (e.g. within a factor of ten), however coliforms and E. coli should be absent (i.e less than 1 per 100ml).

Do point-of-use water heaters present a risk?

Answer
Provided that they are used frequently and the temperature is set to deliver at a minimum of 50 oC, the legionella risk may be regarded as negligible.
At temperatures above 50 oC the risk of scalding increases and, where users are particularly vulnerable to scalding, 50 oC may be too hot.

What is the correct temperature for hot water in a care home, to control the risk of legionella and avoid the risk of scalding?

Answer:
In care homes such as those for elderly or disabled people, there is a greater risk of scalding than for an average population so scald protection is normally required. Unfortunately, water temperatures which are safe in the sense that they do not constitute a scald hazard are unsafe in that they can support legionella bacteria, so the solution is blending.
Hot water should be stored at 60 oC and distributed without blending so it returns to the calorifier (water heater) at no less than 50 oC. Where there are users who are at risk of scalding, thermostatic mixing valves (TMVs) should be installed at, or close to, each tap, shower etc. TMVs blend the hot water at 50 oC plus with cold water at 20 oC or less to deliver water at a safe temperature as follows:-

Application Temperature/ oC
Bidet 38 (40)
Shower 41 (43)
Washbasin 41 (43)
Bath 44 (46)

(Temperatures in brackets are the maximum permitted in the event of a cold water failure).

The length of any blended water piperun should be kept to a minimum, no more than 2m.

  Is water testing for legionella or with dipslides necessary or desirable in a care home for the elderly?

Answer: Dipslide testing is not advocated for tap water systems, hot or cold, tanks, cylinders, showers etc., because the test is not sufficiently sensitive to detect the very low levels of bacteria likely to be present.
However if there is cause for concern over the water condition, or temperature, sampling and analysis in a laboratory for total bacteria levels (TVC) or specifically for legionella should be considered.

TVCs and dipslides do not detect legionella.

 

Further Questions will be added as appropriate

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