Go on. Have a look under your deck. Really look. You’ll probably find a few cobwebs. Maybe a lost tennis ball. Possibly the remains of a kids’ toy that didn’t survive last summer. And a whole lot of dry, dusty, absolutely nothing. Most Australians with a deck, a raised home, or a high-set Queenslander have a void under their property that does precisely nothing. It’s not beautiful. It’s not useful. It just sits there, quietly wasting its potential. So here’s a question worth asking: what if that scrappy patch of dirt was actually worth real money? Because it could be. In fact, with the right under deck water tank in place, it absolutely is.
The Problem With ‘Wasted Space’
Australian property is expensive. Most of us know exactly how much our home cost, what our rates are, and what our mortgage repayments look like. Yet somehow, the space directly under our feet — sitting there doing nothing, year after year — never gets counted.
That void under your deck or elevated home has real value. It’s sheltered from the sun, protected from the elements and out of the way. In short, it’s the perfect place to tuck away a tank. An under deck water tank uses that forgotten space to collect and store rainwater from your roof. Free water, falling from the sky, captured and held for when you actually need it. No yard space used, views lost and no compromise on how your property looks. And here’s where it gets interesting: that stored rainwater has a genuine dollar value that grows every single year.
Water Bills Are Going One Way — And It’s Not Down
Water prices across Australia are climbing. In Sydney, IPART approved a major tariff increase from October 2025, with the average household bill tipped to rise from around $1,220 to $1,388 in the first year alone — and further increases of around 5% annually are locked in through to 2030.
Brisbane households are already paying between $240 and $500 per quarter. The national average sits at around $235 per quarter. These aren’t small numbers — and they’re trending upward every year. So any water you don’t buy from the tap is money you keep. It’s that simple.
What Could You Actually Save?
Let’s run some real numbers. The average Australian home uses around 900 litres of water per day. Outdoor watering alone — lawns, gardens, washing the car — makes up a huge chunk of that. In fact, using tank water for the garden alone can reduce total mains usage by up to 40%. Go further and plumb your underdeck tank into the laundry or toilet, and the savings stack up even faster. Many households who do this cut their mains water use by half or more.
Even conservatively — say, reducing your quarterly bill by $80 to $100 by supplementing garden and laundry use with tank water — you’re looking at $320 to $400 per year in savings. For a 5,000-litre under deck tank priced at $3,425, that’s a payback period of roughly 8–10 years. After that, it’s pure saving for the lifetime of the tank, which is backed by a 10+10-year warranty. And with water prices rising each year, those savings only grow alongside them.
Your Roof Is Already Collecting It — Just Not Storing It
Here’s something that often surprises people. Every time it rains, your roof is already collecting thousands of litres of water. Right now, that water runs straight into the stormwater drain and disappears forever.
The maths are eye-opening. A standard 200m² roof in a region that receives just 600mm of annual rainfall can collect up to 120,000 litres of water per year. Even a smaller 150m² roof in a coastal area getting 800mm of rain could capture the same. That’s an enormous volume of free water going absolutely nowhere.
An under deck tank captures a portion of that — typically 1,000 to 5,000 litres at a time — and holds it ready for when you need it. You can also link multiple tanks together for greater total storage. The water is yours. You’ve already ‘collected’ it on your roof. You’re just not keeping it yet.
Why Autumn Is the Perfect Time to Install
Autumn is genuinely the smartest season to install a water tank in Australia — and most people don’t realise it. First, the weather is milder. Installation is easier and more comfortable for everyone involved. Second, the tail end of the wet season means your new tank can start collecting immediately, so it’ll be full — or close to it — well before summer arrives.
Third, and most importantly, you’ll be set up before the dry season bites. Summer is when water restrictions are most likely, water bills spike with garden use, and the cost of mains water feels most acute. Installing now means you’re already ahead of the problem — not scrambling to solve it in January. In short, Autumn is the time to act. Spring is when everyone else thinks about it. That’s already too late.
So, What Exactly Is an Under Deck Water Tank?
An underdeck water tank is a specially designed low-profile poly tank built to fit beneath a deck or elevated home. Unlike round tanks that stand tall in the yard, under deck tanks are engineered to be extra slim in height — typically 710mm to 950mm — so they slide neatly into the void beneath your property.
The Water Tank Factory offers a range of Duraplas underdeck tanks, from the compact 1,000-litre model right through to the 5,000-litre Lattice™ Underdeck Tank. All are made from heavy-duty, UV-stabilised virgin-grade polyethylene — the same tough material used across the full tank range — and all come with a 10+10-year warranty.
The Lattice™ Underdeck Tank: Built for Tight Spaces
The standout products in the range are the LUD3000 and LUD5000 — the Lattice™ Under deck Tanks. These use patented Lattice™ technology to deliver high-volume storage in a genuinely low-profile design, built specifically for under-deck and under-house installations.
The LUD3000 holds 3,000 litres and sits at just 900mm high. The LUD5000 stores 5,000 litres at 950mm high. Both are strong, light, space-efficient, and completely out of sight once installed. The 5,000-litre model in particular is an ideal choice for unit developments and homes on small blocks with big water needs.
For even greater storage, multiple under deck tanks can be linked together. So that scrappy patch of dirt could, in theory, hold 10,000 litres or more — all hidden away beneath your home.
What Can You Use the Water For?
The short answer: quite a lot. Rainwater stored in an under deck tank can be connected to a range of household uses, depending on how you set things up. The most common applications are:
- Garden watering and lawn irrigation
- Washing the car, boat, or outdoor furniture
- Toilet flushing (with appropriate plumbing)
- Laundry (washing machine use)
- Full household use, including drinking water (with filtration and appropriate setup)
Even using tank water purely for outdoor purposes makes a meaningful difference. Add toilet flushing and laundry into the mix, and you’re replacing a significant chunk of your mains water usage with free rainwater every single week. Plus, during water restrictions — which historically arrive in summer and drought periods — your tank water is yours to use regardless. That flexibility alone is worth something.
‘Small Block, Big Home’ — Sound Familiar?
One of the most common barriers to installing a water tank is space. Suburban blocks are getting smaller, backyards are shrinking, and there often simply isn’t room for a traditional round tank without sacrificing usable yard space. That’s exactly the problem the Lattice™ Under deck Tank was designed to solve. If your yard is too tight for a conventional tank, or if you’d rather keep your outdoor area free for family and entertaining, the space under your deck becomes the answer.
It’s also worth noting that not all spaces under a deck are created equal. The Water Tank Factory’s underdeck range caters to a variety of dimensions. The slimmer 1,000-litre and 2,000-litre models are designed to fit between the piers of existing decks. The larger Lattice™ models suit properties with wider clearance under the floor. The team at The Water Tank Factory can help you work out which model fits your specific space.
Putting a Number on That Patch of Dirt
So let’s go back to the original question. What is that scrappy patch of dirt under your deck actually worth?
Here’s a simple way to think about it. If your under deck tank saves you $350 per year on your water bill — a modest estimate based on current national averages — and your tank carries a 10+10-year warranty, you’re looking at up to $7,000 in water savings over the life of the tank. For a tank that costs between $1,150 and $3,425, that’s an impressive return from a space that was previously earning you absolutely nothing.
Add to that the value of water independence during summer restrictions, the environmental benefit of capturing rainwater before it hits the stormwater drain, and the feel-good factor of making proper use of wasted space — and the case becomes even stronger. That dirt patch? It’s not scrappy at all. It’s an untapped asset.
Ready to Put That Space to Work?
The Water Tank Factory has been helping Australians make the most of their properties since 1984. As a family-owned, factory-direct manufacturer, the team knows their tanks inside and out — and they’re here to help you find the right under deck solution for your space, your budget, and your water goals.
Browse the full under deck range online at watertankfactory.com.au/types/
1300 826 532. Order online and save — with factory-direct pricing and a committed delivery date provided at the time of ordering.
Stop leaving money under the deck. It’s time to put that space to work.