Why councils choose ozone
Chlorine remains the workhorse disinfectant for distribution residual, but it has serious limitations for primary disinfection. Chlorine cannot reliably kill Cryptosporidium — the pathogen behind some of the worst waterborne outbreaks in New Zealand's history — without dosing levels that produce unacceptable disinfection by-products (THMs, chlorates, bromates). Ozone inactivates Cryptosporidium at practical CT values, kills Giardia in seconds, and destroys taste-and-odour compounds (geosmin, MIB) that chlorine cannot. Importantly, ozone is normally used in combination with chlorine — ozone as the primary disinfectant at the plant, chlorine for distribution residual. This dual-barrier approach is increasingly the standard recommended by Taumata Arowai for surface-water and high-risk groundwater supplies.
Designing for DWSNZ and Taumata Arowai compliance
New Zealand's drinking-water regulatory framework — the Drinking-water Standards for New Zealand (DWSNZ), now administered by Taumata Arowai — requires demonstrable log reduction credit for protozoal and viral pathogens. CT-value tables in DWSNZ assign specific log credits for different ozone concentration × contact time combinations at known temperatures. Our engineering team designs every council system to a defined log-credit target, with full CT-value modelling documented in the design package. We provide the design rationale, validation testing protocol and ongoing operational monitoring requirements needed for the council's drinking-water safety plan and water-supply assessor approval. Where retrofitting an existing plant, we work with the council's existing PLC/SCADA architecture and operator workflows.
What a typical council ozone plant includes
A standard council ozone plant comprises: a PSA oxygen generator (or liquid O₂ supply) sized for peak ozone demand; one or more corona-discharge ozone generators with N+1 redundancy where critical; an ozone contactor (typically bubble-diffuser with multiple stages, sized for the required CT value); residual ozone monitoring at multiple points; quench/destruct chemistry where residual must be removed before distribution; ambient ozone detectors in every ozone-wetted room; thermal or catalytic ozone destruct on off-gas; full PLC control with HMI and SCADA integration into the council's existing telemetry; remote monitoring access for both council staff and our service team. Plants are designed for 25+ year service life with major component refurbishment scheduled at 7–10 year intervals.
Smaller supplies and rural communities
Not every supply is the size of Timaru or Whanganui. We supply ozone plants to small community supplies (a few hundred connections), marae, schools and rural lifestyle developments where Taumata Arowai compliance still applies. For smaller flows we deploy compact, skid-mounted ozone plants that fit inside a standard shipping-container building or a small purpose-built plant room. These systems use the same engineering principles and compliance documentation as our larger plants — just sized appropriately. We're often the most cost-effective compliant solution for supplies that are too small to justify large traditional treatment plants but still need primary disinfection with full protozoal credit.
Operator training and ongoing support
Council water-treatment operators are skilled professionals who don't need vendors telling them how to do their job — but ozone is a specialist technology and most water operators have far more experience with chlorine and UV than with ozone. Every council installation includes on-site operator training, a clear O&M manual written for water operators (not chemical engineers), a 24-month commissioning support period, and ongoing scheduled service. We attend the council's water-supply assessor audits and Taumata Arowai compliance reviews when invited, and our engineers are on-call to support during any compliance event or sample failure. This long-term partnership is what councils tell us is the single biggest difference between us and offshore equipment suppliers.
