Monitoring stagnation

Monitoring stagnation within a facility’s water distribution system should aim to reduce water residence time within a water distribution system. This has the following advantages:

  • it reduces the potential for biofilm formation within the water distribution system
  • it ensures any disinfectant residual either introduced or already in the water distribution system will more effectively control microbial load and growth and
  • for the hot water system, it ensures that heated water remains hot enough to prevent Legionella regrowth before delivery to the TMV or (for untempered uses) to the outlet.

It is not possible to monitor stagnation directly, and so other indicators can be used such as:

  • decline in disinfectant residual (e.g. from entry or dosing point to the sample location)
  • increase, or level of, overall bacterial load at the sample point (usually measured via heterotrophic colony count)
  • room occupancy records or records maintained by the staff responsible for routine flushing of outlets in the bathrooms of unoccupied rooms.

When to monitor stagnation control

Monitoring for stagnation within your water distribution system should be ongoing with results appropriately recorded. The frequency for the monitoring of stagnation:

  • for water supply to outlets should be undertaken weekly to prevent the formation of dead legs and
  • in storages should be undertaken in accordance with your water risk management plan (WRMP) and should be at least annually.

Routine flushing should prevent stagnation at outlets and can be combined with routine temperature and disinfection residual monitoring, as detailed in your WRMP.

Operational exceedances, events or situations that could require more frequent stagnation control monitoring (reliance on storage during periods of water supply disruption, refurbishment or building works) should be noted in your WRMP and should include, but not be limited to:

  • flushing of outlets that are not in weekly use
  • inspection of storages during extended periods of hot weather (heating of cold water supplies)
  • other disruptions that may cause changes in water residence time within the facility.

Where to monitor stagnation control

Monitoring stagnation relies on the accurate identification of all the components within your water distribution system. It should, at a minimum, be undertaken at:

  • all plumbing fixtures which are not used weekly
  • the ends of long lengths of plumbing pipework, without outlets
  • water storages, such as potable cold water tanks and potable hot water storage heaters.

Ideally areas of stagnation should be removed or designed out of your water distribution system.

Who should monitor stagnation control

Monitoring stagnation control should be undertaken by trained and competent staff. A workplace health and safety officer should be consulted before carrying out any flushing as personal protective equipment (PPE) may be required (scald protection).

Control measures

See the routine flushing, remedial flushing – operational exceedance and remedial flushing for Legionella information sheets for control measures for preventing stagnation in the facility water distribution system.

Record keeping

In accordance with your WRMP, when carrying out stagnation checks, ensure you record which outlet or storage was checked and/or flushed (e.g. room 15, shower hot water tap), by whom, the location, date and time and any additional comments.

Caution

  • Some stagnation in the water distribution system may be unavoidable.
  • Any capped or plugged pipe ends, which cannot be flushed (e.g. where a fixture has been removed), should be disconnected as close to the supplying water main as possible.
  • Visibly dirty storages should be cleaned and disinfected immediately.
  • Discoloured or odorous water flushed from outlets indicates the potential stagnation of the line. If there is no disruption to the water supply or quality the outlet should be flushed until the water runs clear and odour ceases.
  • Some fire hose reel systems may be connected to a facility’s potable water supply. A backflow prevention device should be installed on the fire hose reel supply pipe as close as possible to the connection to the potable water supply. Backflow prevention devices need to be annually tested to ensure they are operating correctly. This is required to prevent possible backflow of stagnant water from the fire hose reel service, into the potable water supply. Alternately, each fire hose reel should be flushed weekly.

Resources

Last updated: 29 June 2017