Monitoring disinfection residual

Ideally, every healthcare facility should receive town water from their drinking water service provider with a disinfectant residual (usually chlorine-based) sufficient to suppress Legionella proliferation within the facility (see chlorine dosing). However, there is no regulation of disinfectant residuals in Queensland drinking water supplies and so, in many cases, there will be insufficient residual disinfectant to ensure effective suppression of Legionella throughout the full extent of the facility water distribution system.

In very large hospitals, with complex water distribution systems, it can be very difficult, if not impossible, to maintain an effective disinfectant residual throughout the entire facility at all times and so some form or disinfectant dosing may be needed.

Monitoring disinfection residual within your water distribution system is therefore necessary to verify that the facility is operating with an effective disinfection residual, which has the purpose of controlling microbial load, minimising biofilm development and demonstrating compliance with your water risk management plan (WRMP).

When to undertake disinfection residual checks

Checking of water disinfection residuals in the cold, warm and hot water outlets and storages should be taken at the frequency as detailed in your WRMP (but at least monthly).

Routine monitoring of disinfectant residual can be carried out in conjunction with your routine flushing and temperature monitoring programs, as detailed in your WRMP.

Operational exceedances, events or situations that may require more frequent disinfection residual checks should be noted in your WRMP and should include, but not be limited to:

  • low room or ward occupancy resulting in water stagnation
  • water disinfection residuals outside a set critical limit or range
  • other disruptions that may cause changes in water disinfection residual (e.g. plumbing maintenance, an interruption to supply event or advice from the drinking water service provider of a water quality incident).

Where to undertake disinfection residual checks

Disinfection residual checks need to be taken that are representative of the system performance and control. For this reason selecting disinfection residual sampling points is a critical step in the process.

Disinfection residual checks should be taken at predetermined sentinel outlet sampling points, which would usually be located at distal points in the water distribution system or close to high risk locations within the facility.

Hot or warm water from a system that has a flow and return loop:

Take a minimum of 3 disinfection residual checks from each loop or building wing. If the building has multiple floors on a single loop, take 3 disinfection residual checks per floor. One disinfection residual check should be taken from an outlet located close to the start of the flow loop exiting from the hot water supply. Another disinfection residual check should be taken from an outlet located approximate mid-point in the flow loop. The final disinfection residual check should be taken from an outlet location close to the end of the flow loop, prior to the return to the hot water supply.

Hot or warm water from a system that has no flow and return loop:

Take a minimum of 3 disinfection residual checks from each hot or warm water system. If the building has multiple floors with single hot/warm water distribution systems, then take 3 disinfection residual checks per floor. One disinfection residual check should be taken from an outlet located close to the hot water supply (proximal sample). Another disinfection residual check should be taken from an approximate mid-point in the system. The final disinfection residual check should be taken from an outlet location close to the furthest point from the hot water supply (distal sample).

Cold water system:

Take a minimum of 3 disinfection residual checks from each system or building wing. If the building has multiple floors, take 3 disinfection residual checks per floor. One disinfection residual check should be taken from an outlet location close to the entry point from the mains incoming cold water supply (proximal sample).  Another disinfection residual check should be taken from an approximate mid-point in the system. The final disinfection residual check should be taken from an outlet location close to the furthest point from the mains incoming cold water supply (distal sample).

Who should undertake disinfection residual checks

Disinfection residual checks should be undertaken by competent staff using appropriate equipment. Swimming pool test kits or test strips should not be used. A workplace health and safety officer should be consulted before carrying out disinfection residual checks as personal protective equipment (PPE) may be required (for scald protection).

Steps

Main steps for monitoring disinfection residual should meet the following criteria:

  • For hot water storage the disinfection residual can be checked by operation of the heater’s pressure relief valve. Alternately, locate the nearest hot water outlet to the heater to record the disinfection residual.
  • For cold water storages, record the disinfection residual by partially opening the tank’s drain valve and record the disinfection residual at the discharge into the drain. Alternately, locate the nearest cold water outlet to the storage tank to record the disinfection residual.
  • For tap outlets the procedure is the same for both the hot or cold water supplies:
    • run the outlet for 60 seconds to allow the water to reach a stabilised disinfection residual. Note: some hot/ warm water outlets may take longer to reach a stabilised disinfection residual.
  • Carry out disinfection residual testing as per the instructions specific to the system you are using (e.g. photometer).
  • Once completed, ensure the outlet is turned off and any water splash is mopped up.

Control measures

See chlorine dosing and control measures information sheets for possible control measures for maintaining the water distribution system disinfectant residual within acceptable limits.

Record keeping

In accordance with your WRMP, when carrying out disinfection residual checks, ensure you record which outlet was checked for disinfection residual (e.g. shower, hot water tap), by whom, the location, date and time and any additional comments.

Caution

  • Stringent control measures must be implemented to prevent the risk of scalding.
  • Throughout the disinfection residual recording process, exposure to aerosols should be minimised.
  • Collection of samples for laboratory analysis of disinfection residuals (e.g. copper silver ionisation) will require the appropriate sampling container, as advised by the laboratory that will analyse the samples.

Resources

Last updated: 29 June 2017