• Water testing at commissioning 
• Routine water testing
• Frequency of testing 
• Microbiological limits
• Selection of outlets for sampling
• Interpretation of routine water testing results

 

It is important that responsibilities for routine and ad hoc water testing are well defined by the Water Safety Group.

Each NHS board should have processes in place for the receipt, reporting and distribution of results which should include as a minimum:

• escalation of out of specification results. Exceptions should be recorded and rapidly disseminated to all WSG members and local IPC team (a record should be kept of distribution lists for reporting)
• clear responsibilities should be defined for interpretation and action of results

Water testing at commissioning

• In order to ensure IPC input and oversight of risk, IPC teams should be involved in the design and planning process and engaged through to commissioning and handover. This includes agreeing acceptable water sampling parameters and remedial actions to be taken if results are unacceptable.
• A full set of the analysed water sample results should be approved by the WSG before handover and before the system is brought into clinical use
• The WSG should confirm water is of potable quality and meets other minimal water testing requirements with clinical and microbiological oversight from the ICD/microbiologist on behalf of the WSG.
• After water system replacement/remedial activities, water sample analysis results should be approved by the IMT/ WSG or agreed local process.

What to test

A sampling plan with appropriate microbiological parameters and should be agreed by WSG prior to tender. As a minimum it should include testing in all settings for:

• Total Viable Counts (TVCs)
• coliform bacteria (including E.coli)
• Legionella spp.

Testing for P. aeruginosa should be carried out in high-risk settings.

Local risk assessment should determine if there are additional testing requirements.

When to test

Samples should be taken no sooner than five days and no later than seven days after a full disinfection process has been completed and a further set of samples should be taken immediately prior to handover.

• Analysis should be carried out by an independent accredited laboratory (United Kingdom Accreditation Service (UKAS) or ISO 9002). See SHTM 04-01 Part C.

Actions following commissioning results

As part of their commissioning water safety plan, the NHS board should have pre-agreed processes in place should the results of commissioning tests be unsatisfactory. For more details on commissioning, see SHTM 04-01 Part A and BS 8680.

Routine water testing

Results from routine water testing over time (trend analysis) provides evidence of effective control measures and also supports early detection of HAI risks.

What to test

The WSG should agree the routine water testing required and this should form part of the water safety plan. As a minimum:

• routine water testing should be undertaken for Pseudomonas aeruginosa and Legionella species in high-risk settings and areas where high-risk patients are treated
• a local risk assessment according to BS 8580-1 and BS 8580-2 should be undertaken to assess the need for routine water testing in other care areas and for organisms other than Legionella and Pseudomonas aeruginosa
• consider trend analysis for Total Viable Counts (TVCs) to monitor water quality as this may indicate when results are deviating from what is considered normal for that particular water system
• equipment and/or medical procedures that use water which is separate from the main hot and cold water distribution system should be routinely tested in line with relevant guidance/manufacturer’s instructions which includes:
  • water for heater cooler units (NHSScotland Guidance for Decontamination and testing of Cardiac Heater Cooler Units (HCUs)
  • water used for renal dialysis 
• Where no UKAS accreditation exists for routine testing of specific healthcare water system-associated microorganisms, boards should still consider testing. The UKAS Technical Bulletin highlights the following important points.
  • There will always be new and emerging organisms causing outbreaks, for which there will not yet be established or accredited methods but where microbiology testing laboratories play a vital role in determining the source of infection.
  • There is significant risk to patients if sources during outbreaks are not detected and mitigated against. The lack of UKAS accreditation for a specific test does not preclude laboratories from processing these samples. Such specimens can be processed provided the laboratory states on the report that the test is not UKAS accredited.

Frequency of testing 

As a minimum, testing for P. aeruginosa and Legionella spp. in high-risk settings should occur every 6 months.

The frequency of routine microbiological water testing in other areas and for other microorganisms should be based on a comprehensive risk assessment undertaken by the WSG.

Increases to the frequency of water testing should occur:

• during a suspected or confirmed outbreak where a link to the water system is being explored or considered
• if surveillance identifies an increased incidence of infection known or suspected to be associated with the water system
• after implementing any changes to the water system for example after biocide dosing, remedial works or a refurbishment project
• when thermal or chemical controls have failed or are failing (for example when levels of biocide are lower than the agreed limit)

Consideration should be given to increasing the frequency of routine water testing when pre-flush trend analysis demonstrates increasing colony forming units (cfu)/100 ml for P. aeruginosa.

Microbiological limits

Healthcare water systems

Recommended microbiological limits for water samples are detailed in the table below.

Note: Incubate drinking water system samples at 22˚C and 37˚C for 24 hours in accordance with BS EN ISO 6222.

Microbiological limits for healthcare water systems

Pathogen	Colony Forming Units (CFU)
Coliform bacteria (including Escherichia coli)	0 cfu/100ml
Enterococci	0 cfu/100ml
P. aeruginosa	0 cfu/100ml
Legionella spp.	Undetectable in high-risk units. <100 cfu/litre in non-high-risk units
Legionella pneumophila serogroup 1 (Lp1)	Undetectable
For all other gram-negative healthcare water system-associated organisms	0 cfu/ml

 

Additional microbiological limits 

The table below details recommended additional microbiological limits for water samples obtained from water dependent equipment.

Recommended additional microbiological limits for healthcare procedures that present an increased risk

Procedure	Colony Forming Units (CFU)	Total Viable Count  (TVC)	Endotoxin
Heater cooler unit water	0 cfu/100ml for Mycobacterium spp.	TVC cut-off levels of <100 cfu/ml	None
Hydrotherapy water	<20 cfu/litre for Legionella spp. 0 cfu/100ml for Staphylococcus aureus as part of wider investigations only (local decision)	TVC cut-off levels of <10 cfu/ml	None
Endoscopy final rinse water	0 cfu/100ml for Mycobacterium spp.	TVC cut-off levels of <10 cfu/100 ml	Endotoxin limit of <0.25 EU/ml
Final rinse water in surgical instrument washer disinfectors	TVC cut-off levels of <1 cfu/100 ml	None	Endotoxin limit of <0.25 EU/ml
Renal dialysis fluid and water	TVC cut-off levels of <50 cfu/ml	None	Endotoxin limit of <0.125 EU/ml

 

 

Selection of outlets for sampling 

For routine testing, samples collected should be pre-flush only unless otherwise directed by the WSG/IPCT or Microbiology.

• Pre-flush sampling in a busy ward may have to occur early in the morning or at another time when water outlet usage is lower.
• Pre-flush samples should be taken by collecting water straight from the outlet as it is first turned on.
• Pre-flush samples may help to identify colonisation in a particular outlet.

If post-flush samples are to be taken, the sample should be collected after first running the outlet to flush through the pipes. Post-flush samples may support differentiation between local and systemic colonisation following a positive pre-flush result (see BS 7592 for more information).

A planned targeted sampling plan should be developed by the WSG to include:

• up-to-date schematic of the systems, including identified sampling points
• risk assessment and identification of water sampling requirements which ensure areas identified as high-risk in terms of patient susceptibility are included
  • high-risk also includes areas supporting microorganism growth for example cooler parts of the hot water system or warmer parts of the cold water system

Take samples from the proximal and distal ends of each water system with a locally agreed number of sampling points between.

• The number of samples collected during any single round of sampling should be sufficient to be fully representative of the entire water distribution system.
• The outlets being sampled within clinical facilities should be rotated at each sampling round unless a decision has been made to sample all outlets every time.
• Outlets within ancillary facilities (including those shared by departments) such as staff kitchens, domestic services rooms (DSR), treatment rooms and preparation rooms, should be tested during every round of routine sampling.

Interpretation of routine water testing results

• Responsibilities for receiving and initial interpretation of water results should be agreed by the WSG and included in the WSP. This should include agreed processes for escalation of out of specification results.
• Any test results which are above the agreed microbiological limits should be escalated for attention by the Infection Prevention and Control Doctor and Consultant Microbiologist and the AE (water) where required.
• The clinical risk associated with the sample location should be considered when interpreting results.
• If water test results are above the microbiological limits, the following environmental factors should be reviewed to assist with interpretation of results (the water system’s schematic diagram may support this process):
  • water temperature
  • pH
  • residual disinfectant
  • water softeners
  • water turnover
• Routine water test results should be interpreted as a series of trends (over time) and with an awareness of the systems schematic and current condition.

Sampling results and actions following a non-compliant result (no patient cases)

• If coliforms are identified in a water sample, a repeat sample should be collected and tested to rule out a false positive.
• Whenever pre-flush sample results remain above the microbiological limits, pre- and post-flush samples should be collected to determine if there is a local or systemic contamination. Where post-flush samples remain above microbiological limits, it may indicate systemic contamination. Negative or low post-flush samples may indicate a local contamination (outlet and/or associated pipework and/or fittings near the outlet).
• Taking water samples from further back in the system (beyond the outlet itself) should be considered when positive pre-flush and post-flush sample test results are obtained.
• Following a positive water test result, an immediate review of existing control measures and risk assessment by the IPC team and estates team should be carried out to identify additional remedial/clinical actions required.
• If water continues to test positive following remedial intervention at the outlets, consider taking water samples from further back in the system (beyond the outlet itself).
• Repeat samples should be taken when disinfection/remedial actions have taken place to ensure effectiveness of actions.

Remedial actions following positive water results (no patient cases)

Remedial actions should be agreed by the WSG.

Remedial actions should be determined based on consideration of the water test results in context with the water system as a whole, any existing control measures, and the areas where the result has been obtained.

• When post-flush samples are negative or have low counts, remedial actions should be directed towards the outlet (and associated pipework and fittings).
• When attempting to remove or reduce microbial contamination at the outlet (inclusive of the drain) consider:

• • disinfection (chemical and/or heat treatment),
  • physical replacement of parts of the outlet
  • removal of the entire outlet (including dead-legs)
• If contamination is suspected to extend beyond the outlet (further back in the system) whole system water disinfection may be required.

For more information on whole water system disinfection see  (SHTM 04-01 part D ‘Disinfection of Domestic Water Systems’