Multi-unit waterways calculator

This calculator covers dual occupancy through to multi-story apartments.

Use this spreadsheet to calculate the water consumption of Multi Unit Residential development with and without water saving features (i.e. Pre2003 water consumption).

Information required when using the calculator

  • Number of bedrooms
  • Water rating for shower head, dishwasher, toilet and clothes washer
  • Site area
  • Total roof area
  • All rainwater tank information
  • All grey water system information and
  • Any swimming pool, spa or pond information.
  • Lawn area
  • Garden area
  • Impervious surface area

Additional information

Information for multiple rainwater tanks or multiple greywater tanks can be grouped together if the size, collection area and end uses of the water sources are equivalent, for example:



If there is multiple rain water tanks and they all have 100m2 of roof area flowing into them, they are all 2000L in Volume and are all used for garden irrigation, toilet flushing and cold water laundry,

Then the volumes can be considered as one tank and collection area can be considered as one roof. This principle only works if all of the volumes, roof area end uses are equal. If this is not the case, then they need to be considered separately.


Download the calculator (XLS 13.9MB)

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