Finishing construction and being ready to supply drinking water are two different milestones. A tank fresh off installation, or freshly relined, still carries construction residue, new-material off-gassing potential, and an unproven microbiological baseline — all of which commissioning exists to address before the tank goes into potable service.
Construction residue and new-material effects
Welding residue, dust, and manufacturing or installation debris are a normal byproduct of construction — not a defect, but something that must be physically removed before the tank holds drinking water. Some new materials, including certain liners and coatings, can also require an initial curing or off-gassing period, and flushing period, before water quality stabilises to normal service levels.
Disinfection establishes a safe microbiological baseline
A newly constructed or relined tank has no established microbiological history — disinfection (commonly chlorination to a specified concentration and contact time) is the standard method for establishing a safe baseline before the tank is connected to the potable network, consistent with AS/NZS 3500 and related guidance.
Clean, disinfect, flush
The tank interior is cleaned of construction debris, disinfected to the specified chlorine concentration and contact time, then flushed and refilled with potable-quality water — a sequence, not a single step, and skipping or shortening any part of it undermines the whole process.
Water quality testing before handover
Samples are tested against the relevant water quality parameters — typically including microbiological indicators, disinfection residual, and turbidity — before the tank is confirmed ready for service. Handover without confirmed test results is handing over an assumption, not a verified outcome.
Commissioning is the step that turns a finished structure into a verified water asset. A tank handed over without documented disinfection and water quality results is handed over on trust, not on evidence.
| Item | Why it matters |
|---|---|
| Cleaning of construction debris confirmed | Removes physical residue before disinfection begins |
| Disinfection concentration and contact time recorded | Verifies the disinfection process met the specified standard |
| Flushing completed before final sampling | Removes disinfection byproducts and residual chemicals before service |
| Water quality test results against relevant parameters | Provides objective evidence the tank is safe for potable service |
| Commissioning records retained with as-built documentation | Supports future compliance review and asset history |
Does a relined tank need the same commissioning process as a brand-new tank?
Yes. A relined tank has a new internal surface in contact with potable water, and the same cleaning, disinfection and testing sequence applies before it is returned to service, regardless of whether the surrounding structure is new or existing.
What water quality parameters are typically tested before handover?
Commonly microbiological indicators, disinfection residual, and turbidity, though the specific parameters and acceptance criteria should be confirmed against the applicable standard and any project-specific requirements before commissioning begins.
Can a tank be connected to the network before commissioning is complete?
No — connecting a tank to a potable network before disinfection and water quality testing are confirmed risks introducing construction residue, disinfection byproducts, or an unverified microbiological risk into the wider supply. Commissioning should be fully completed and documented before connection.
Commissioning a new or relined potable water tank? A properly sequenced and documented process protects both water quality and your compliance position.
Discuss tank commissioning