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Chemical clean

A chemical clean removes deposits and established biofilm in contaminated water distribution systems which enhances the effectiveness of subsequent disinfection processes and may improve flow rates where heavy biofilm contamination has developed.

What is chemical cleaning

The process involves injection into the water distribution system of a chemical agent, often a highly alkaline detergent-based chemical.

When selecting the cleaning agent, compatibility of the cleaning agent with a wide variety of materials used in water distribution systems should be considered, such as any existing disinfection and the type of piping (e.g. PVC, copper etc.) used in in water distribution system.

Chemical cleaning should be consistent with the manufacturer’s recommendations for specialist equipment installed into the water distribution system, such as macerators, dental units and endoscopes, to prevent damaging the equipment.

Newer, environmentally friendly chemical cleaning agents are now also available, but their efficacy is still being established.

Any chemical used for pipe cleaning (or other purposes) must have a material safety data sheet available on site.

Who undertakes a chemical clean

The facility’s water risk management team and a workplace health and safety officer should be consulted before carrying out a chemical clean.

A specialised, suitably qualified and competent professional should undertake a chemical clean, such as water treatment specialist.

Before starting a chemical clean, an assessment of the entire plumbing system should be undertaken to avoid unintended chemical exposure to patients/residents and to prevent damage to the water distribution system or building. The assessment should include all fittings and associated equipment as well as proposed control and prevention measures to guard against chemicals being sent to unintended locations in the water distribution system.

Water distribution infrastructure equipment may need to be disconnected during the chemical clean process. Warranties should be checked to ensure equipment is not exposed to chemicals at a level that will damage them.

When to undertake chemical clean

A chemical clean should only be undertaken after a thermal clean and superchlorination have failed to remove Legionella.

Where to undertake chemical clean

Depending on the size, complexity and ability to isolate the water distribution system, a chemical clean may affect an entire facility or only a limited number of outlet(s) in a localised area (e.g. single wing, ward or cluster of rooms). All sensitive equipment should be identified and disconnected during the cleaning process.

Ideally, a risk assessment should be conducted before implementing a chemical clean, considering both the water system and patient risk, owing to the potentially harsh nature of the cleaning agents.

A chemical clean may require temporary evacuation of occupied areas (or at least secure restriction of access) during the process to prevent any accidental use of water while it is unsafe for use.

During the clean it is essential to tag out all outlets. Each outlet should have a record sheet attached. This should not be removed until all work is completed and, in the case of a detection, until resample results are clear.


The main steps in an alkaline chemical clean would include:

  • Ensure that all staff involved wear appropriate personal protective equipment (PPE).
  • In all facilities, especially those older than 20 years, if possible plumbing should be checked to ensure it is in an acceptable operating condition and free of excessive corrosion or wear.
  • An alkaline detergent is dosed into the water distribution system in all targeted areas.
  • Flush every outlet downstream of the dosing point until it is obvious that the chemical has reached every outlet.
  • Obtain an appropriate concentration (usually pH 10) at each outlet; then shut the outlet to maintain that level continuously for at least 30 minutes.
  • The cleaning chemical only needs to be used in those parts of the water distribution system (including compatible fittings) where biofilm build up is known to be a problem.
  • Flush the treated section of the water distribution system until pH less than 8 is achieved at each outlet, and the water is free from any discolouration or odour.
  • Record the degree of contamination (by noting water colour and particulate matter) flushed from each fitting. This can be achieved by noting the time taken until normal water quality is achieved.
  • After the chemical clean (which removes deposits and established biofilm in contaminated water distribution systems), the water distribution system should be chlorinated again.
  • Flush the treated section of the water distribution system again using water from the regular drinking water supply until 6.5 < pH < 8.5 and free chlorine < 5 mg/L are achieved.
  • Resample the water to determine if the microbial quality is acceptable. If this has not been achieved, repeat the chemical clean and superchlorination of the affected outlets.


  • Residual alkaline detergent is corrosive and can cause serious harm if not managed properly.
  • Take all reasonable and necessary precautions to protect building staff and patients/residents from the risk of exposure to the alkaline detergent and/or any other cleaning or disinfecting chemicals that are used. Note that this includes the installation of backflow protection devices and injection points in a manner such that areas of the facility can be isolated for proper, individual cleaning events.
  • In older building systems where pipe work may be ageing, or where mixed metals may have been installed over time, chemical cleaning may stimulate irreversible corrosion causing rapid water distribution system failure.
  • Where large volumes of the cleaning agent are required, trade waste approval from the relevant sewerage service provider may be required to discharge treated water to the sewer system.


Last updated: 29 June 2017