Farm water calculator

The water calculator tool has been developed to assist with planning water supplies on-farm.

The figures and formulas used within the tool are based on best science at this time. Due to the variable nature of water and the assumptions contained within the science, these figures should be used as a guide only.

Please Note: Personal monitoring of farm water use, storage and supplies should be done in conjunction with this tool, to provide a real-time and more accurate picture of the situation.

Farm water calculator: the annual balance

The farm water calculator can be used to determine:

  • how much water is used on the property
  • how much water can be stored on the property
  • the potential supply of water from a range of sources, such as shed roofs, waterways, groundwater and/or catchment runoff
  • how long the available water will last on the property
  • how farm water supplies cope under different rainfall scenarios.

There are 2 key methods for monitoring water:

Method 1: Manual flow rate measurement

  1. Collect water in a container (bucket or barrel) of known volume
  2. Time how long it takes to fill the container using a stopwatch
  3. Calculate flow rate using the formula:

    Flow rate (L/min) = volume (L) / time (min)

  4. Estimate total usage by multiplying the flow rate by the duration each outlet runs.

Method 2: Tank volume monitoring

This method uses:

  1. water tank levels (before and after usage) to estimate volume used
  2. supply data (e.g. from rainwater collection or mains input) to track inflow
  3. volume calculations based on tank dimensions or level sensors.

Calculations used in the tool rely on ‘field measurements’ of on-farm water storages and supplies. For assistance with these measurements, please refer to the field measurements guide.

This information may be of assistance to inform decision-making, however the State of Victoria and its officers do not guarantee that the information is without flaws of any kind or is wholly appropriate for your particular purpose or situation. This disclaims all liability for any error, loss or other consequence which may arise from use or reliance on this information.

Start farm water calculator

Water use on-farm

Please fill in the following sections with information relevant to your farming situation. The figures can be altered by typing over the default value, which have been provided as a starting point. Your own measurements and observations should be used preferentially.

Please Note: The units used within this calculator are megalitres. One megalitre is equal to 1,000,000 litres.

The rainfall figures below will populate based on your selected location. Try a range of yearly rainfall and evaporation rates for your property to see the effect on the water budget. For additional locations go to Bureau of Meteorology web-site. View the information in a table format

* Individual data may be entered, if known

Property details are required to complete the supply and storage sections of the calculator.

The livestock drinking figures below will prepopulate based on your livestock type and sub-type. View the information in a table format

Household water use

Garden water use

The Garden water use figures below will prepopulate based on your garden type and area.
View the information in a table format

Error: Annual evaporation (mm/year) and Annual average rainfall (mm/year) has not been entered in the property details section (Step 2).

No value for the evaporation losses can be populated below without this figure.

Dairy shed water use

Dairy shed water use is highly variable and where possible your individual water use should be calculated using the Measuring water use in the dairy booklet. This number should then be entered directly into the Megalitres/year field. Alternatively, the drop down lists can be used to provide a reasonable estimate of water use.

The Dairy shed water use figures below will prepopulate based on your dairy type and herd size.
View the information in a table format

Other water uses may include spraying, cleaning equipment, cleaning feedpads, or fire-fighting. Water use for other on-farm activities can be manually measured using the Measuring Water Use in the Dairy which steps through a flow rate and tank volume measuring method. Alternatively, an estimation can be manually entered.

Important to Note: licences can be required for certain water uses on-farm, depending on the water source. Contact your local water corporation for more information about licensing requirements.

Potential water supply on-farm

If you don't know how much water can be supplied from creeks, rivers and bores you may need to manually measure this. Measuring Water Use in the Dairy steps through a flow rate and tank volume measuring method or check on your water authority licence.

Error: Annual evaporation (mm/year) and Annual average rainfall (mm/year) has not been entered in the property details section (Step 2).

No value for the evaporation losses can be populated below without this figure.

If you don't know how much water can be supplied from roof surfaces you may need to manually measure this. Measuring Water Use in the Dairy steps through a flow rate and tank volume measuring method or check on your water authority licence.

The rate and volume of runoff from a catchment for stock and domestic use is highly variable.
Please refer to Determining Catchment Yield for planning farm dams.

The Potential catchment supply figures below will prepopulate based on your catchment area/feeding dam, soil profile, ground cover, average rainfall & location (from step 2).
View the information in a table format

Error: Annual average rainfall (mm/year) or Location North/South of Divide has not been entered in the property details section (Step 2). No value can be populated below without this figure.

Water Storage On-Farm

The Dam volume supply figures below will prepopulate based on your annual average rainfall & annual average PAN evaporation in step 2.
View the information in a table format

Error: Annual evaporation (mm/year) and Annual average rainfall (mm/year) has not been entered in the property details section (Step 2).

No value for the evaporation losses can be populated below without this figure.

Dam water totals

Please note: The dam calculations assume a batter slope of 3:1.

The gully dam formula applies only to water in and above the excavation. Measurements must match the excavation, not the total water area.

Please refer to the following:

Overall Summary

Total on-farm Water use

Overall Potential Water Supply

Overall farm water storage

The Farm Water Balance

In dry periods, reduced rainfall leads to minimal runoff into dams and catchments, and creeks may cease to flow. The Farm Water Balance compares on-farm water storage (such as in dams and tanks) with annual water usage. It's especially useful in regions where water supply is unpredictable or seasonal.

Farm water balance Water Storage on-farm - Water use on-farm
Farm water balance No value set - No value set
Farm water balance megalitres/year

Surplus

A surplus occurs when the total on-farm water storage capacity exceeds the farm's annual water requirement. Providing storages are full at the beginning of the year, the properties water requirements can be met.

Deficit

A deficit arises when the farm's annual water requirement exceeds the available on-farm storage. When facing a water deficit, consider the following:

  • Does the water source reliably refill storages throughout the year, ensuring water needs are met in most seasons?
  • Is there enough water available in some years but not others, leading to occasional shortages?
  • Does the property experience water shortages nearly every year, indicating a persistent and recurring shortfall?

Step 1 / 6

Page last updated: 05 Aug 2025