Watercalcs
Estimates only — verify before relying on results. Terms of Use
2.2
i What this tool does & how to start ▶

This is a preliminary design and operating-guidance tool for ultraviolet (UV) treatment — both disinfection (a pathogen barrier) and advanced oxidation (UV-AOP) for taste/odour and micropollutant destruction. It helps you scope reactor sizing, chemistry, and running costs before you talk to suppliers.

Start here on Setup: choose your operating mode, lamp type and reactor arrangement, then enter your flows and source-water quality. The other tabs update automatically.

  • Disinfection — sizing guidance against the NZ DWQAR 2026 UV rules and the required log credits for your source-water class.
  • AOP — hydroxyl-radical chemistry and % destruction of geosmin, 2-MIB, algal toxins, NDMA and atrazine.
  • H₂O₂ Mgmt — sizing the peroxide quench (chlorine, GAC or bisulfite).
  • OPEX — energy, lamp/ballast/sensor replacement and chemical running costs.
  • Report & Save — the only place to export a PDF, download CSV, or save/load your work as a file.

New to it? Flick the example switch below to load a worked case and see every tab populate. Turn it off to clear back to a blank sheet.

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Guidance only — not a validation. This tool does not validate UV equipment and makes no validation claim. UV disinfection performance and log-credit validation are the responsibility of the equipment supplier, who must provide a validation certificate to a designated standard (USEPA UVDGM, DVGW, ÖNORM, DIN, or NSF/ANSI 55 Class A). Required doses for any log-credit claim come from the specific unit's certificate — not from this tool.
Show worked example Loads a representative surface-water UV/AOP case across every tab. Turn off to clear all inputs.

Operating mode

Dual sizes the reactor for disinfection and evaluates AOP destruction at the applied UV energy.

Lamp & reactor

Flow

L/s
L/s
L/s
%
Utilisation = fraction of the year the plant produces water (drives energy & consumables).

Source water quality

%
NTU
mg/L
mg/L
pH
mg/L
Alkalinity as mg/L CaCO₃. DOC and carbonate are the main hydroxyl-radical scavengers in AOP.

Foulants (quartz sleeve scaling) drives sleeve-cleaning method — which must be part of the validation

mg/L
mg/L
mg/L
mg/L
Fe, Mn and hardness deposit on sleeves and cut UV transmission. High values point to a wiper and/or chemical (CIP/OSS) cleaning system — see the fouling guidance on the Disinfection tab.

Disinfection context sets the required protozoa log credit (DWQAR rule 8 / T3.PC.2)

The tool tailors monitoring & dose-control guidance to the standard. The certificate itself comes from your supplier.

Target contaminants for AOP destruction (optional)

ng/L
ng/L
µg/L
ng/L
µg/L

Live check

i Disinfection — purpose & how to read it ▶

This tab helps you scope a UV disinfection barrier and lines the design up against the NZ Water Services (Drinking Water Quality Assurance) Rules 2026 — the UV rules (T3.BU) and protozoa UV rules (T3.PU), in force 1 July 2027.

  • Your source-water class (set on Setup) fixes the protozoa log credit you must provide: Class C → 3-log, Class D → 4-log.
  • The general disinfection barrier requires a reduction-equivalent dose (RED) of at least 40 mJ/cm² for ≥95% of production time (T3.BU.4).
  • For a protozoa log-credit claim, the required RED is whatever the specific unit is validated to deliver — you enter that value from the supplier's certificate. The indicative doses shown are typical UVDGM figures for orientation only.

The sizing figures below are preliminary hydraulic guidance to help you shortlist units and estimate power. They are not a validation and do not replace the supplier's certified flow-vs-dose envelope.

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All validation is done by the supplier. The required RED for any log credit is set by the unit's validation certificate. Figures here are indicative sizing guidance only.

Target dose basis

mJ/cm²
Leave blank to use the indicative UVDGM value for your required log credit as a placeholder.

Preliminary sizing margins indicative capacity derating

×
×
Used only to derate preliminary hydraulic capacity. The certified envelope already embeds validation factors.

Required & sizing

Indicative organism doses USEPA UVDGM 2006 — reference only

OrganismLog creditIndicative RED (mJ/cm²)

Preliminary capacity envelope

Indicative max flow per duty unit vs UVT (at target RED)
Indicative only — the certified flow-vs-UVT-vs-dose envelope from the supplier governs.

Sleeve fouling & validation envelope what must be reflected in the supplier's validation

Sleeve fouling. Iron, manganese and hardness precipitate on the quartz sleeves and reduce UV transmission, so the delivered dose falls between cleans. The UVI sensor should see this, but only if the duty sensor is trended and alarmed.

Cleaning system is part of the validation. If fouling control is required, the unit must be validated with that system operating as it will in service:

  • Wiper systems — mechanical wipers (and any wiper cycle interval) must be included in the validation. A UV validated without a wiper cannot claim credit when run with one, and vice-versa.
  • Chemical / CIP / on-line sleeve cleaning (OSS) — if chemical cleaning is used to hold UVT, the cleaning regime and its recovery must be demonstrated; the validated dose applies to the fouled-sleeve condition the certificate specifies.

Hydraulics and configuration must match the validation. UV validation is specific to the tested geometry and flow field. The following must be the same in service as in the validation certificate, or the credit does not hold:

  • Reactor orientation and layout — horizontal vs vertical, and inlet/outlet configuration (straight, L- or U-bend) including upstream/downstream straight lengths.
  • Approach velocity / flow range through the reactor, and the flow-vs-UVT-vs-dose envelope.
  • Lamp type, sleeve, and any wiper or cleaning system as noted above.

This tool does not validate any of the above. Confirm each item against the supplier's validation certificate to a designated standard (USEPA UVDGM, DVGW, ÖNORM, DIN, or NSF/ANSI 55 Class A).

DWQAR 2026 monitoring & compliance checklist

    i Advanced oxidation (UV-AOP) — purpose ▶

    UV-AOP pairs UV light with an oxidant (H₂O₂ or pre-formed chlorine) to generate hydroxyl radicals (•OH) — an aggressive, short-lived species that destroys taste-and-odour compounds and micropollutants that survive conventional treatment.

    • Scavenging — DOC and carbonate/bicarbonate soak up •OH and set how much oxidant and energy you need. High-alkalinity, high-DOC waters are harder.
    • Two destruction pathways — •OH attack plus direct 254 nm photolysis. NDMA is destroyed mainly by direct photolysis, so it behaves differently from geosmin/2-MIB.
    • % destruction is estimated at the applied UV specific energy you set below.

    These are literature-kinetics estimates for scoping. Site-specific performance should be confirmed by bench/pilot trials.

    Oxidant

    mg/L
    mJ/cm²
    Typical UV/AOP: 400–1000 mJ/cm² (much higher than the ~40 mJ/cm² disinfection barrier)

    Hydroxyl radical budget

    ScavengerConc.k(•OH)Scav. rate share

    Contaminant destruction at applied energy

    ContaminantInOutLog% destroyed

    Sensitivity

    % destruction vs applied UV specific energy

    By-product & process notes

    i H₂O₂ management — purpose ▶

    When you dose hydrogen peroxide for AOP, most of it survives the reactor and must be removed before the water enters supply. This tab sizes the quench.

    • Chlorine — reacts with H₂O₂ (roughly 2.1 g Cl₂ per g H₂O₂ by stoichiometry; dose higher in practice). Simple, but consumes chlorine.
    • GAC — catalytically decomposes H₂O₂ at short contact time. No added chemical, but media replacement cost.
    • Bisulfite — chemical reduction. Also scavenges dissolved oxygen.

    Applies to UV/H₂O₂ mode. UV/chlorine and UV-only modes leave no peroxide residual to manage.

    Quench method

    g/g
    Stoichiometric ≈ 2.09 g/g; use 2.5–3.0 to allow for demand.

    Residual & sizing

    Method comparison

    MethodSizing basisConsumableNotes
    i Operating cost — purpose ▶

    Estimates annual running cost: energy, lamp / ballast / UVI-sensor replacement, and any AOP chemicals and quench consumables. Prices and component lives live in the ⚙ Settings panel so you can tune them to local rates.

    Use it to compare LPHO vs medium-pressure, or disinfection-only vs AOP, on a whole-of-life basis. Figures are indicative and exclude capital, labour and maintenance overheads.

    Cost inputs defaults in ⚙ Settings

    $/kWh
    ×
    $/kg
    $/kg
    $/kg

    Annual operating cost

    Cost breakdown

    Component$/yrShare

    10-year projection

    i Summary — purpose ▶

    A one-glance roll-up of the design: dose basis, reactor sizing, AOP destruction, operating cost and the key DWQAR 2026 compliance points. Use it as the cover sheet when you take the scheme to suppliers or reviewers.

    i Report & Save — purpose ▶

    The single place to get your work out of the tool.

    • PDF report — a clean, printable summary. Tick the sections you want, then Generate.
    • CSV — all inputs and headline results as a spreadsheet.
    • Save file — downloads a .json holding every input and result. Keep it, share it, or load it back later to pick up where you left off.

    Choose sections to include

    PDF report

    Generates a formatted report of the selected sections. Use your browser's “Save as PDF” in the print dialog. Header/footer are off by design — turn off “Headers and footers” in the dialog if your browser adds them.

    CSV download

    All inputs and headline results as a single CSV.

    Save & load

    Save a JSON file of all settings and results to your downloads, or load one back in.

    About & model basis

    Settings & variables