Plan for Volume | Rain Harvesting Steps | BMCo

Plan for volume

Obviously, you can’t control the rain. However, that doesn’t mean you can’t harvest and store enough rainwater to meet your needs.

Understanding how much rainwater you can harvest, how much water you require and how you can minimise water loss allows you to design a Rain Harvesting system that provides adequate water for all your planned rainwater uses.  By designing for volume in this way, you can ensure you harvest as much rainwater as possible – and have somewhere to store it.

268 TWA 0638 Round

In particular, we recommend doing all you can to account for challenges posed by:


Vegetation         Unwelcome Intruders

Fine Particles      Hidden Activity


Calculate what you can harvest 

The volume of water you can harvest largely depends upon your rainfall (measured in mm over time) and your roof size (measured in square metres).  

National or local weather services such as the Bureau of Meteorology in Australia can provide historical rainfall data for your area, while you can calculate your roof size by looking at your building plans or using Google Maps 

Calculate your water needs 

Past water bills, estimates based on the factors above or data from meters and gauges can all help you more accurately forecast your water needs.   

Suhyeon Choi 433995 Unsplash
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Plan for seasonality 

If you experience seasonal rainfall or your peak rainfall and water use times differ, you’ll want bigger tanks to capture enough water for drier times.

You will also want to ensure you have connected as much roof area as is practical to your tank.  

Specify your system 

Balancing the volume of rainwater you need with the volume you can harvest will inform your decisions regarding tank numbers and size. You should also design your Rain Harvesting system with appropriate products to minimise water loss.

Products that can help

Maelstrom Filters
Maelstrom Filters
Tank Level Gauges
Tank Level Gauges
Tank Overflows and Screens
Tank Overflows and Screens

Find out more about applying the 8 Rain Harvesting Steps

Download the
Rain Harvesting Handbook


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