Getting started
What this tool does. It projects water demand for a district year by year over the horizon you choose and compares it with what each treatment plant, its sources and its treated storage can supply. The outputs are trigger years (when a limit is reached), decision years (when work must start, allowing for lead time), the size of the increment needed, and insights that flag unusual inputs or cheap alternatives such as leakage reduction. Use it for master planning of new sources, plants, expansions and reservoirs.
How the pieces fit. Supply zones are groups of people and businesses (a town, a holiday settlement, a growth cell), each with its own growth, water use and firefighting class. Each zone is served by a treatment plant. Each plant has one or more sources (river, bore, lake) with daily and annual take limits, plus treated storage and a leakage figure. Upgrades are staged additions to a plant.
Where to start. Work left to right through the tabs: Setup (start year, horizon, plants, zones), Growth (population change per zone), Demand (water use per zone), Capacity (each plant's sources, treatment, storage, losses and upgrades), Results, then Report & Save. Every zone and plant appears as its own block with a status badge, so you can see what is still to do. Each tab has its own guide at the top.
The two icons top right. The i button opens "About this Model": what is calculated, the equations, assumptions, limitations and public references. The gear opens Settings: flow units, scenario spread, peak factors, dependable capacity factor, storage target hours, firefighting basis and the lead times used for decision years. Defaults are typical NZ practice; change them to match your organisation's standards.
Not sure? Switch on the worked example above, look through each tab, then switch it off. Your work is saved in this browser automatically; use Report & Save to keep a file.
Step 1: Project and time frame
Step 2: Treatment plants
One row per treatment plant, or per group of plants feeding one connected network. Sources, capacities, storage, losses and upgrades for each plant are entered on the Capacity tab.
Step 3: Supply zones
Split the population wherever growth, water use or firefighting class differs. Assign each zone to the plant that supplies it. Growth and water use are then set zone by zone on the next two tabs.
Guide: using this tab
Each zone has its own block below; its badge shows whether growth has been set. Two ways to describe growth: growth rate by period (type an annual % for each period, or fill from a profile and edit) or projected population (type the population you expect at the end of each period, for example Stats NZ subnational projections, medium series). Blank years are interpolated in a straight line between the years you enter; after your last entry the last growth rate continues.
What you enter is the medium case. Low and high growth apply the scenario spread from Settings either side. Long-run NZ district growth is typically 0 to 1.5% a year; rates above 3% for decades are unusual. Known developments that add a set number of people belong on the Demand tab as step loads, so they are not double-counted here.
Guide: using this tab
Each zone block turns people and activity into water: residential use per person (with an optional demand-management target), non-residential demand and growth, and visitors where the zone has a holiday population. Per-capita figures are customer consumption; leakage is entered per plant on the Capacity tab, so do not include it here.
Where peaking is applied. Each group peaks on its own terms and the model adds them: the residential peak day factor applies to resident consumption only, the non-residential factor to commercial and industrial demand, and visitor demand enters at its full peak-day value because the visitor figure you give is already the busiest day. So enter each zone's peak visitors or carry the holiday swing in the residential factor, never both. For a zone with visitors entered, keep the residential factor at the everyday urban value (1.5 to 2.0); only where you leave peak visitors at zero should the residential factor rise to 3 to 5 to stand in for a holiday population.
Firefighting class (SNZ PAS 4509) sets the fire reserve the zone's storage must hold in addition to balancing and emergency storage. Step loads at the bottom are known future additions with a start year.
Planned developments and large users
Known future additions with a start year. A population step load (people) uses its zone's per-capita rate and peak factor. A flow step load (average day flow) carries its own peak day factor, typically 1.0 to 1.3 for industry.
Guide: using this tab
Each plant has a block below. Enter its sources (each with a maximum daily take and, where consented, an annual take), treatment installed capacity, treated storage and non-revenue water. The dependable factor in Settings derates treatment for maintenance and a unit out of service. Storage is checked against the hours-of-demand target in Settings plus the firefighting reserve for the zones served.
Upgrades are staged additions with the year the capacity becomes available. Add them to test a programme and watch the trigger years on Results move. The capacity check at the bottom of each block shows today's demand against each limit.
Guide: using this tab
The three growth buttons. The rates and populations you entered on the Growth tab are the medium case. Low and high re-run the whole projection with every zone's population growth rate shifted down and up by the scenario spread in Settings, so a zone entered at 1.1% a year is run at 0.6% and 1.6%. Nothing else moves: non-residential growth, visitor growth, per-capita and leakage targets, step loads and all capacity stay as entered, which is why the grey band on the chart is population uncertainty only. In projected-population mode the tool takes the implied rates from the populations you typed and shifts those, so low and high are derived from your medium series rather than being a separate published series.
Choose a growth scenario and a plant (or the whole project). The demand and capacity chart is the core output: demand rising against dependable treatment capacity and source take. The grey band around the demand line is the uncertainty range: its upper edge is demand under high growth and its lower edge under low growth, so the wider the band, the more the timing depends on which growth case turns out to be right.
Actions required answers three questions for each constraint: what has to be done, the year demand passes the limit, and the year work has to start for it to be in service by then (limit year minus the lead time in Settings). It also splits the size of the job into what is needed by the limit year and what is needed by the end of the horizon, so a large requirement can be staged rather than built in one go. Insights flag unusual inputs and cheaper alternatives; everything below that is supporting detail.
Status colours: green = no action needed in the horizon, amber = work must start within about three years, red = the start date has already passed or the limit is already exceeded, grey = not entered.
Demand and capacity outlook
Actions required
For each constraint: what would have to be built or consented, the year demand passes the limit, the year work has to start so it is ready in time, and how big the job is at each point.
Insights
Prompts to look more closely, not verdicts. Thresholds are general NZ practice and should be tuned to your system.
Supporting detail
Where the water goes
Production by component at the start year and the horizon. A large loss share or visitor share shows where the cheapest capacity is.
Projection table
Guide: using this tab
Choose which parts to include, then export a PDF report (your browser's print dialogue; choose "Save as PDF") or a CSV of the year-by-year projection for every plant and all three scenarios. Save writes everything you entered, plus settings, to a JSON file in your downloads folder; Load restores it later or on another device. This is the only place the tool exports from.
Report contents
Reports
The PDF covers every plant under the scenario selected on Results. The CSV contains every plant and all three scenarios, one row per year.
Save and load
Your work is also kept in this browser automatically. Save a JSON file before clearing data (Setup tab) or moving to another device.