In a country as dry and climate-variable as Australia, storing water efficiently isn’t just wise—it’s essential. While above-ground rainwater tanks are a common sight in rural and urban properties, underground rainwater tanks are becoming increasingly popular for homeowners who want reliable water storage without sacrificing space or street appeal.
This comprehensive guide will walk you through everything you need to know about underground rainwater tanks in Australia: from their benefits and cost comparisons to legal compliance, installation, and maintenance. If you’re considering going underground, this post will help you make the most informed decision.
Why Choose an Underground Rainwater Tank?
An underground water tank allows you to store thousands of litres of clean water beneath your property—without impacting your landscaping, outdoor space, or property design. They’re ideal for small blocks, urban infill developments, and any property where above-ground tank placement is impractical.
Key benefits:
- Completely hidden from view
- Frees up space in yards and driveways
- Protected from sunlight, reducing algae growth
- Maintains cooler, more stable water temperature
- Safer in bushfire zones (less likely to melt or crack)
- Complies with BASIX requirements in many urban councils
Whether you’re harvesting water for garden irrigation, toilets, laundry, or bushfire preparedness, underground tanks offer all the functionality of traditional tanks—minus the bulk.
Above-Ground vs Underground: Which is Right for You?
| Feature | Above-Ground Tanks | Underground Tanks |
| Visibility | Fully visible | Fully hidden |
| Space Usage | Takes up yard or patio space | No above-ground footprint |
| Installation Cost | Lower | Higher (excavation required) |
| Maintenance Access | Easier | Requires surface access lid |
| Bushfire Resilience | Exposed to fire and heat | Protected underground |
| Temperature Stability | More prone to heat | Cooler, stable water |
If discretion, space-saving, or compliance with development guidelines is important, underground tanks are worth the extra upfront cost.
What Size Underground Tank Do You Need?
Popular underground rain tank sizes include:
- 3,000L (ideal for small households or garden use)
- 5,000L (suitable for average suburban homes)
- 10,000L+ (recommended for large households or rural properties)
Calculate your ideal tank size by factoring in:
- Your average rainfall (in mm)
- Roof catchment area (in m²)
- Water usage needs (garden, toilet, laundry, etc.)
Formula: 1mm rain on 1m² roof = 1 litre of water.
Legal Requirements & Council Compliance
In many parts of Australia, especially NSW and Victoria, underground rainwater tanks must comply with local council regulations and development codes.
Key compliance considerations include:
- BASIX (NSW) water-saving targets
- Distance from property boundaries
- Stormwater detention requirements
- Load-bearing capacity for trafficable lids
- Access for inspection and overflow prevention
Check with your local council or ask your installer to ensure all guidelines are met. In Sydney, for instance, under-deck or underground tanks are often the only viable solution for meeting BASIX targets in compact developments.
What Makes a Good Underground Tank?
When shopping for an underground tank, make sure it’s:
- Trafficable (if being installed under a driveway or parking area)
- Low-profile design for easier excavation and installation
- Fitted with reinforced lids and risers
- Manufactured from food-grade polyethylene
- UV-stabilised and engineered for in-ground pressures
The Water Tank Factory’s Lattice™ Underground Tanks tick all these boxes—offering 3,000L and 5,000L options built to handle Australian soil conditions and vehicle loads.
Explore the full range here: Underground Water Tanks
Installation: What to Expect
Installing an underground tank is more involved than an above-ground one, but entirely manageable with the right team. It typically involves:
- Excavation to the required depth and dimensions
- Base preparation using compacted sand or crusher dust
- Tank placement with adequate bedding and levelling
- Backfilling with sand or stabilised fill
- Fitting accessories (inlet strainer, overflow, outlet, pump)
- Connection to household or irrigation system
You may also require council inspection, stormwater integration, and pump housing installation, depending on your location.
Maintenance Tips
Even though underground tanks are largely set-and-forget, basic maintenance ensures clean, reliable water:
- Check leaf strainers and first-flush diverters quarterly
- Flush sediment from tank annually
- Inspect risers and lids for sealing and integrity
- Clean gutters regularly to avoid organic contamination
Pro tip: install a first-flush diverter to significantly reduce sludge and bacteria buildup.
Cost of Underground Water Tanks: Is It Worth It?
Underground tank systems can cost more upfront due to excavation, installation, and access fittings. However, they provide permanent, hidden water storage that adds to property value and meets long-term sustainability goals.
Typical starting prices:
- 3,000L Lattice™ Tank: From $2,800–$3,400
- 5,000L Lattice™ Tank: From $3,600–$4,400
Ask about site-specific freight and installation quotes when ordering.
Why Choose The Water Tank Factory?
- Australian-made tanks engineered for underground conditions
- Trafficable lids and compact designs for under-driveway or yard installs
- 10+10-year warranty on poly construction
- Factory-direct prices with Australia-wide delivery
- Expert advice from a team who understands local requirements
Explore your options today: Underground Rainwater Tanks
Or if you would like to talk to one of our friendly team direct, we would love to hear from you. CALL US NOW: 1300 826 532