Water Main Disinfection & Chlorination (AS/NZS 3500.1) SWMS

Water main disinfection covers the disinfection of new and repaired water mains before they are placed into service — charging the main with a chlorine-based disinfectant solution, holding it for the required contact time, and flushing and confirming the water quality before the main supplies drinking water. It is water-quality-critical work that uses concentrated chlorine-based disinfectants, which are hazardous chemicals that can cause chemical burns, respiratory harm and, if not neutralised before discharge, environmental harm to waterways. This document is written on the basis that water main disinfection is carried out by competent personnel with the chlorine-chemical, water-quality, neutralisation and environmental hazards controlled.

Water main disinfection is carried out in connection with AS/NZS 3500.1 and the water utility's requirements, using chlorine-based disinfectants to disinfect the main. The disinfectant chemicals are hazardous chemicals managed under the hazardous-chemicals provisions, with the high-strength chlorine solution requiring careful handling, and the chlorinated water requiring neutralisation before discharge so it does not harm waterways. The water quality is confirmed before the main is placed in service. This document coordinates the chlorine-chemical, water-quality, neutralisation and environmental controls so the main is disinfected and the supply protected.

Hazards identified

9 hazards covered, sorted by priority.

Control measures

Hierarchy-of-controls order: elimination → substitution → isolation → engineering → administrative → PPE.

1. 1Administrative: handle the chlorine-based disinfectant as a hazardous chemical to its safety data sheet, with the high-strength solution prepared, dosed and handled carefully, and the chemicals not incorrectly mixed.
2. 2PPE: chemical-resistant gloves, eye and face protection, and respiratory protection appropriate to the chlorine where vapour or gas is possible, per the safety data sheet and AS/NZS 1715 and AS/NZS 1716.
3. 3Engineering: disinfect the main to AS/NZS 3500.1 and the water utility's requirements — charging with the disinfectant at the required concentration, holding for the required contact time, and flushing.
4. 4Administrative: neutralise the chlorinated water before discharge so it does not harm waterways, and dispose of or discharge the neutralised water in accordance with the environmental requirements.
5. 5Administrative: confirm the water quality — disinfection and any required testing — before the main is placed in service, so the main supplies safe drinking water.
6. 6Engineering: manage the stored pressure and water of the charged main, controlling the release, and apply the confined space and access controls where the work at the main is confined or below ground.
7. 7Engineering: use mechanical aids for the chemicals and equipment, and control contact with the chlorinated water during charging and flushing.
8. 8Administrative: ensure the work is carried out and certified by an appropriately licensed plumber or drainer under the relevant state or territory plumbing licensing scheme, with the relevant competencies and a compliance certificate issued where required.
9. 9Administrative: all workers must hold a valid White Card (General Construction Induction Training, CPCCWHS1001) where the work is construction work, with the plumbing, confined space and any other competencies required for the work.
10. 10Administrative: conduct a pre-start toolbox talk covering the day's work, identified hazards, isolations, required PPE and emergency procedures, and record attendance in the consultation section.
11. 11Administrative: consult workers and any health and safety representatives on the work and its risks, record the consultation, and keep this document available at the workplace.
12. 12PPE: eye protection to AS/NZS 1337.1, hearing protection where required, gloves appropriate to the task, high-visibility clothing, and Class I or Class II safety footwear with protective toecap to AS/NZS 2210.3.
13. 13Administrative: review and update this SWMS whenever the work scope changes, after any incident or near miss, when a worker or health and safety representative raises a concern, when new hazards are identified, or at minimum every 12 months.

Applicable Codes of Practice

Worked example

A water contractor is engaged to disinfect a new water main before it is placed in service. The chlorine-based disinfectant is handled as a hazardous chemical to its safety data sheet, with the high-strength solution prepared, dosed and handled carefully and the chemicals not incorrectly mixed, and chemical-resistant gloves, eye and face protection and respiratory protection appropriate to the chlorine worn. The main is disinfected to AS/NZS 3500.1 and the water utility's requirements, charging with the disinfectant at the required concentration, holding for the required contact time, and flushing. The chlorinated water is neutralised before discharge so it does not harm waterways, and the neutralised water disposed of in accordance with the environmental requirements. The water quality is confirmed — disinfection and any required testing — before the main is placed in service. The stored pressure and water of the charged main are managed, controlling the release, and the confined space and access controls applied where the work is below ground. The main is disinfected and the records retained.

Related legislation

• Model Work Health and Safety Act — primary duty of care; the duty to consult workers; the reckless-conduct offence; and notifiable-incident provisions, as enacted in each jurisdiction.
• Model Work Health and Safety Regulations — Section 291 high risk construction work and the SWMS preparation and review duties, and the confined space and hazardous chemicals provisions where applicable, as enacted in each jurisdiction.
• The relevant plumbing and drainage standards AS/NZS 3500 (Parts 0–5), AS/NZS 1547 for on-site wastewater, AS/NZS 4233 for high-pressure water jetting, and the hazardous chemicals and environmental requirements, are called up by the relevant legislation, together with the relevant network utility and asset owner requirements.
• Plumbing and drainage work is licensed under each state and territory's plumbing licensing scheme, with the relevant competencies for confined space and chemical work, and compliance certification required for notifiable work; electrical work is carried out by a licensed electrician.
• Victoria operates under the Occupational Health and Safety Act 2004 and the Occupational Health and Safety Regulations 2017, with the high risk construction work, confined space and hazardous chemicals provisions applying in place of the model instruments.

Frequently asked questions