Chemical Cleaning of Potable Water Systems
Chemical cleaning is not a common practice in potable water systems. When selecting the cleaning agent, you must consider the compatibility of the cleaning agent with the wide variety of materials used in a potable water systems.
Chemical cleaning is a common practice in industrial and process water systems such as cooling and wastewater systems. The process involves circulation of a chemical agent to remove biofilm, scale and deposits. Removing these deposits improves the subsequent disinfection process. The process also improves flow rates and reduces stagnation
Chemicals used may be alkaline such as caustic soda. Acidic treatments include sulfamic acid or organic such as citric acid. Detergents and surfactants, such as quaternary ammonium compounds, are also in common use. Many of these chemicals are hazardous via ingestion, aerosolisation and skin contact.
Specific chemical cleaning is necessary for some specialised components of facilities such as macerators, dental units and endoscopes. In these cases cleaning should be consistent with the manufacturers’ recommendations.
Advantages of Chemical Cleaning:
Chemical cleaning may remove biofilm and entrenched deposits from pipe surfaces improving water flow rates and reducing stagnation. Removal of deposits can improve the effectiveness of subsequent chemical disinfection processes for control of Legionella and other bacteria.
Chemical cleaning agents are aggressive. Competent personnel with suitable personal protective equipment should handle and use them with appropriate containment. Isolating the water system is essential to avoid exposure of building occupants to the chemicals. This may involve temporary vacation of buildings. Dosing, circulating, dumping and then flushing the entire system with clean water will require large volumes of water . Removal of light deposits may elevate corrosion by oxidising disinfectants.
In older building systems pipe work is often ageing or mixed metals may have been installed over time. In these cases chemical cleaning may lead to spontaneous pipe failures by removing the protective conditioning film on the pipe surface. It may also stimulate irreversible general and galvanic corrosion causing rapid system failure. Using sodium and potassium hydroxide (caustic soda and caustic potash) will de-zincify components of the systems such as galvanised surfaces or brass fittings.
The photograph below shows the after effects of caustic chemical flushing of a potable water system. The corrosion deposits were identified once the flushing procedure had been completed and normal potable supply restored.
Some acidic organic detergents used in waste water and cooling water systems such as citric and oxalic acid may be corrosive.They may also be a nutrient source for microorganisms. So residual concentrations of these chemicals in a potable water system may actually assist their colonisation by harmful bacteria.
There is the potential for exposure of occupants to harmful chemicals or their residuals in the water supply. Discharging large volumes of treated water to sewer. may require Trades Wastes approval from the relevant sewerage service provider.
It is not recommended practice for potable water systems in any Australian jurisdictions or globally to chemically clean potable water systems as a pre-cursor to disinfection. Preferably cleaning agents should be included in the list of chemicals recommended for use in potable water systems in table 8.2 of the Australian Drinking Water Guidelines (see below). In some jurisdictions using chemicals not listed in the table may contravene the State Safe Drinking Water legislation.
‘If a chemical not listed in this chapter is to be used in the treatment of drinking water, it is the responsibility of the water authority to seek advice from the appropriate state or territory health regulatory agency, and to take into consideration health, environmental, and occupational health and safety issues.’
Australian Drinking Water Quality Guidelines 6 2011 Version 3.2 Updated February 2016.
Government of South Australia (2012). Restricted Wastewater Acceptance Framework. https://www.sawater.com.au/__data/assets/pdf_file/0018/6723/Restrictedwastewateracceptanceframework.pdf
enHealth. Guidelines for Legionella control in the operation and maintenance of drinking water distribution systems in health and aged care facilities (2015).
South Australian Government. Safe Drinking Water Act 2011, Safe Drinking Water Regulations 2012.
US EPA Office of Water EPA 810-R-16-001 September 2016, Technologies for Legionella Control in Premise Plumbing Services. https://www.epa.gov/ground-water-and-drinking-water/technologies-legionella-control-premise-plumbing-systems