Water treatment calculators
A calculator and model suite, aligned to NZ and/or global standards. Opmate, our AI operator assistant, is launching soon — join the waitlist below.
The full toolkit for plant operators and designers
Every calculator produces estimates based on real operations and design experience. However, the outputs do not constitute engineering, regulatory, scientific, legal, or other professional advice, and are not a substitute for the judgement of a suitably qualified and experienced professional who has assessed your specific circumstances.
Treatment Process Selector
Recommend treatment process trains based on raw water quality and DWQAR.
Chlorine Demand & DBP Model
Model chlorine residual decay and disinfection by-product formation.
DWQAR Sample Scheduler
Smart sample schedule generator for all supply types for new 2027 DWQAR rules.
Water Chemistry Model
pH, alkalinity,LSI, CCPP, corrosion indices, plant sizing and dosing costs.
Filter Monitoring Tool
Monitor long term performance of filters. Backwash profiles, media depths and dirt content.
Jar Testing Tool
Set up mixing, make solutions, determine dosing regimen and assess results.
Operator Maths Tool
All the maths functions and calcs that operators need to know and use.
Arsenic Tool
Determine arsenic type and assess treatment options for removing.
Nitrate Tool
Determine nitrate/nitrite risk and assess treatment options for removing.
Pump System Calculator
Pump curves, system curves, VSD modelling, costs and surge analysis.
Multi-Criteria Analysis Tool
Make transparent decisions. Set-up, score and assess decision sensitivity.
Plant Hydraulic Model
Determine the hydraulic grade line for gravity flow plants for a range of flowrates.
Tank Sizer
Size tanks & wet wells for continuous and batch operations.
Frontline Operations Staffing Tool
Work out how many frontline staff you need, or assess risk of your current levels.
Plant Mass Balance Tool
Full plant mass and flow balance for a range of scenarios, including residuals management.
Plant Audit Model
Structured audit framework to assess and benchmark plants.
Oxidation Tool
Determine the optimum process for oxidation of Fe, Mn & ammonia.
Compliance Indices Tool
Determine compliance and assurance indices for suppliers, supplies, plants and zones.
Dechlorination Tool
Determine dechlorination requirements and impacts for tanks and pipelines.
PID Tuning Tool
Tune water treatment control loops - flow, level, pressure and feedback dose control.
Critical Control Point Tool
Develop your CCP register and responses based on DWQAR and best practice.
DWQAR Assurance Rule Tool
Develop your assurance and reporting rules strategy and response.
PAC Dosing Tool
Determine PAC dose required for removal of organics contaminants.
Filter Design Tool
Size rapid gravity filters including media, backwash & internals.
MF/UF Membrane Design Tool
Size and manage MF/UF membrane plants including configuration, LRV and repairs.
UV Design Tool
Size and model UV plants for disinfection and advanced oxidation.
Chlorination Design Tool
Size and model chlorine gas and hypo storage, dosing and contact tanks.
Cost Estimating Tool
Create capex, opex and NPVs for multiple options, with multiple contingency models
Carbon Footprint Tool
Create an operational carbon inventory for a drinking water supply, from the source to the tap.
New Source Sampling Tool
Determine the optimum sampling regime for any new source type.
If you have any requests for new tools, want any changes, or spot any bugs we'd love to hear from you.
Meet Opmate — the AI assistant that does the job alongside you.
Calculators give you numbers. Opmate gives you answers. Built on 25+ years of plant operating experience, Opmate troubleshoots issues, runs the calculators for you, and grounds every recommendation in your plant's own documents.
- Diagnoses plant issues conversationally
- Picks the right calculator and runs it for you
- Reads your Ops Manual, WSP, SOPs, and SRMP
- Available on desktop or mobile, on shift
Steps we need to take:
1. Check the poly dose setpoint. For stable conditions it should be around 0.05mg/L.
2. Do a dose time to confirm if the dose pump is delivering this.
3. Check the batching system. We may have made up a batch that is too strong.
Built for operators and engineers
Free to use
Every calculator's basic tabs are free, forever. Premium unlocks advanced tabs.
Expert built
30+ years of operational experience encoded into every formula, default, and assumption.
Mobile ready
Designed for the way operators actually work — on shift, in the field, on a phone.
NZ & global
Tools for both Taumata Arowai / DWSNZ and global standards. Filter by region.
Free to use, Premium to unlock more
Every calculator is free. Most also include advanced features that only unlock with Premium. Any applicable tax is added at checkout.
Premium
Access to advanced calculator features.
- Advanced calculator functions
- Save & import
- PDF & CSV export
Need multiple seats for your team or organisation? See team pricing — from 3 seats, pay by card or invoice.
Watercalcs is brought to you by Dr Jason Colton, a water treatment specialist whose 30-year career spans operations, contracting and consulting, working on treatment plants across the UK, Asia, the USA, Australia and New Zealand. His doctorate is in water process engineering, specialising in filtration.
Common questions
What is Watercalcs?
Watercalcs is a suite of online drinking water treatment calculators for plant operators, engineers and councils. It covers chemical dosing, disinfection, filtration, hydraulics, process design, cost estimating and New Zealand regulatory compliance. Everything runs in a browser with nothing to install.
Who is Watercalcs for?
Water treatment plant operators, process and design engineers, council and council-controlled organisation staff, and consultants working on drinking water supplies. It is built around New Zealand and Australian practice, though most of the engineering tools apply anywhere.
Does Watercalcs cover Taumata Arowai and DWQAR requirements?
Yes. Several tools are built specifically around the New Zealand Water Services Drinking Water Quality Assurance Rules, including a DWQAR sample scheduler, an assurance rule tool, a critical control point register builder and compliance indices. These reflect the 2026 Rules, which come into force on 1 July 2027.
What calculators are included?
Water chemistry and corrosion indices, chlorine demand and disinfection by-products, chlorination and UV design, filtration and membrane design, jar testing and coagulation, pump and hydraulic modelling, tank sizing, mass balance, plant auditing, operator staffing, cost estimating, carbon footprint, and a set of New Zealand compliance tools.
How much does Watercalcs cost?
Every calculator has free basic tabs with no registration required. Premium unlocks the advanced tabs for an individual subscription, and team plans start at three seats with per-seat pricing that reduces as the team grows. All prices exclude applicable taxes.
Can my council or organisation buy Watercalcs for a team?
Yes. Team plans cover three or more people with an administrator who manages who has access. New Zealand organisations can pay by invoice on 30-day terms with a purchase order number, which suits council procurement. Everyone else pays by card or direct debit.
Do I need to install anything?
No. Every calculator runs in a web browser and works on locked-down plant machines without software installation or administrator rights. The tools are also designed to work on a phone, on shift.
Are the calculations reliable?
Each tool states its assumptions and method, and is checked against real plant data before release. The outputs are engineering estimates for comparison and preliminary design. They are not professional advice, and you should verify results against jar testing, plant trials, laboratory analysis and the applicable standards before acting on them.
Who built Watercalcs?
Watercalcs is built by Dr Jason Colton, a water treatment specialist with a 30-year career across operations, contracting and consulting in the UK, Asia, the USA, Australia and New Zealand, and a doctorate in water process engineering specialising in filtration. It is operated by Water Software Solutions Ltd, a New Zealand company.