How Much Rainwater Can You Collect From Your Roof?
Hint: It’s probably more than you think!
When people think about rainwater harvesting, they often ask: “Will I really collect enough water to make it worthwhile?” The answer is a definite yes!
At Designer Tanks, we believe sustainability should be both practical and beautiful. So, let’s break down just how much rainwater you can collect from your roof, and what that means for your home and garden.
A Simple Formula
Here’s a widely used rule of thumb in New Zealand:
1mm of rainfall on 1 square metre of roof = 1 litre of water collected
(Source: Ministry for the Environment – NZ Rainwater Collection Systems Guide)
So if you have a 100m² roof and it rains 10mm, you can collect:
1,000 litres of water
Real-Life Example
Let’s say you have a 150m² roof and live in a region like Hamilton or Wellington, which typically receives around 1,200mm of rain per year. (Source: NIWA Climate Data, 2024).
150m² x 1,200mm = 180,000 litres per year
That’s a significant amount of clean, soft water you can use for:
- Watering the garden
- Washing your car
- Cleaning windows, decks, and outdoor furniture
And all of it comes straight from the sky – free and low in minerals, making it especially gentle on plants and surfaces.
A Few Things to Consider
- Roof material matters: Smooth surfaces, such as metal, collect water more efficiently than textured materials, like tiles.
- Gutters and downpipes: Well-maintained gutters ensure maximum collection and minimal loss.
- Tank size: This depends on how you plan to use your water and the available space. We’re happy to help you choose the right fit!
Why Harvest Rainwater?
- Save money on your water bill
- Reduce pressure on local supply infrastructure
- Keep your garden thriving during dry spells
- Support sustainable living in a stylish way
Want Help Choosing the Right Tank?
We’re here to help. Whether you want to make a design statement or prefer something more discreet, we’ve got options to suit every home.
Browse our designer range at www.designertanks.co.nz or contact us for personalised advice.