It’s not just about saving water, it’s about choosing the right system for how you live.

Across Queensland, more homeowners are turning to rainwater tanks to cut down on utility bills, ease pressure on local supplies, and create drought-resilient homes. But before you invest in a tank, one big question needs answering: How much water do you really need?

At Creek to Coast Plumbing, we help homeowners design smarter rainwater harvesting systems and choosing the right tank size is a crucial first step.

How Much Rainwater Can You Collect?

Start by understanding your collection potential. This depends on your roof area and the average annual rainfall in your region.

Let’s break it down:

• For every square metre of roof space, you can collect about 1 litre of water per 1mm of rain.
• If you have 200m² of roof area and receive 1,200mm of rain a year, that’s 240,000 litres annually (in theory)

But that’s the ideal scenario. In real life, you’ll lose water to first flush systems, evaporation, roof angle, gutter design, and overflow.
We usually recommend allowing for 80–90% collection efficiency.

How Will You Use the Water?

This is where real-world planning matters. Are you collecting water just for the garden — or do you want to supply toilets, laundry, or even your whole home?

Here’s what to consider:

For Garden Irrigation Only

If you’re planning to water lawns, veggie beds, or ornamental gardens, a small to mid-size tank (2,000–5,000 litres) might do the job.
But it depends on the size of the area and your local rainfall pattern.
Short bursts of heavy rain mean larger tanks help capture more when it falls.

For Laundry & Toilet Use

Homes that use rainwater for toilets and washing machines typically benefit from 5,000–10,000 litre tanks. These appliances make up about 35–40% of internal water use, so this can deliver real savings.

You’ll need a pump and proper plumbing to integrate these systems with your house which is something Creek to Coast handles as part of our installation.

For Whole-House Supply

Going completely off-grid or supplying rainwater to every tap? You’ll likely need 20,000 litres or more, depending on household size. Larger tanks also help provide backup for fire safety, periods of low rainfall, or household guests.

How Many People Live in the Home?

A good rule of thumb is to allow around 150–250 litres per person per day if you’re using rainwater for general use.

• For a couple: a 5,000–10,000 litre tank may be sufficient
• For a family of 4+: consider 10,000–20,000 litres or larger

The more people in the home, the quicker your tank will deplete — especially during dry spells.

Is Your Roof Big Enough?

The surface area of your roof determines how much water you can collect.
Bigger roof = more harvesting potential.
But layout matters too. If multiple roof sections can be connected to one tank, we’ll help design a smart downpipe system to capture from as many surfaces as possible.

For smaller homes or townhouses, slimline or under-deck tanks may be a better fit — and Creek to Coast can help find the right option.

Placement, Guttering & Overflows

Rainwater harvesting doesn’t stop at the tank.

A good system needs:

• Secure, well-graded gutters that don’t clog
• Leaf guards and first flush diverters to protect water quality
• Overflow systems directed away from your home’s footings
• A level, reinforced tank pad or stand

Creek to Coast Plumbing offers full rainwater system setups including guttering upgrades, pump connections, stormwater management and filtration, so your tank is safe and future-ready from day one.

Want Cleaner, Safer Rainwater?

We also recommend considering whole-house rainwater filtration, especially if you plan to use your tank for more than just the garden.
Puretec Hybrid Plus systems, installed by our team, can filter out sediment, odour, tannins, bacteria and even adjust your water’s pH to prevent copper leaching and pipe corrosion. Read more about why we suggest water filtration for tank water.

Final Thoughts

Choosing a rainwater tank isn’t about the biggest tank on the market — it’s about matching your system to your roof size, rainfall patterns, and water use habits.

At Creek to Coast Plumbing, we’ve helped Queenslanders build sustainable rainwater setups for over 30 years. From tank sizing and placement to full guttering and filtration systems, we’ll make sure you get the most from every drop.