Above-Ground vs Underground Rainwater Tanks: Which Is Best?

You're not alone. More Australians than ever are turning to rainwater harvesting as a smart way to reduce water bills, become more self-sufficient, and do their bit for the environment. With droughts becoming increasingly common across many parts of the country, capturing rain when it falls just makes sense. But here's the thing choosing between an above-ground and underground rainwater tanks isn't as straightforward as it might seem.

What Is the Difference Between Above-Ground and Underground Rainwater Tanks?

Above-ground tanks sit on a prepared base at ground level, typically connected to your downpipes via a simple diverter system. They rely on gravity to collect water and often use pumps to distribute it around your property. These tanks come in various shapes and sizes, from slimline models that tuck against walls to large round tanks for rural properties.

Underground rainwater tanks, on the other hand, are buried beneath your yard, driveway, or garden. They require excavation during installation and always need a pump to move water to the surface. These tanks are engineered to withstand soil pressure and are typically made from reinforced concrete or heavy-duty polyethylene.

Pros and Cons of Under Ground Rainwater Tanks

Above-ground installation offers several compelling advantages. Installation is straightforward and significantly cheaper than burying a tank. You can easily inspect your tank for damage, check water levels, and perform maintenance without special equipment. Plus, if you ever need to replace or relocate your tank, it's a much simpler process.

However, there are downsides to consider. These tanks take up valuable yard space and can be an eyesore if not positioned thoughtfully. They're also more susceptible to temperature changes water can warm up in summer, potentially encouraging algae growth. In bushfire-prone areas, plastic above-ground tanks pose an additional risk.

Above-ground tanks work brilliantly for:

• Properties with limited budgets

• Homes where easy maintenance access is a priority

• Rural blocks with plenty of space

• Situations where temporary installation makes sense

Pros and Cons of Underground Rainwater Tanks

Underground installation keeps your yard looking pristine. With the tank buried, you can use the space above for gardens, lawns, or even parking. The soil naturally insulates the water, keeping it cooler and reducing algae problems. In bushfire zones, underground tanks offer superior protection.

Underground tanks make the most sense for:

• Urban properties with limited outdoor spaceHomes where aesthetics matter greatly

• Bushfire-prone regions

• Properties where maximising usable yard space is essential

How Long Do Underground Rainwater Tanks Last?

Above-ground poly tanks typically last 15 to 25 years with proper care. Steel tanks can exceed 30 years if well-maintained, while concrete above-ground tanks may last 50 years or more.

Underground rainwater tanks generally enjoy longer lifespans. Protected from UV radiation and temperature swings, quality underground poly tanks often last 25 to 35 years. Concrete underground rainwater tanks can serve you well for 50 years or beyond.

Several factors affect longevity:

• Material quality and thickness

• Installation quality

• Water quality and sediment levels

• Maintenance frequency

• Local soil conditions (for underground tanks)
  

Installation Requirements and Considerations

Site preparation differs dramatically between options. Above-ground tanks need a stable, level base typically compacted crusher dust or a concrete slab. Underground rainwater tanks installation requires excavation, proper drainage consideration, and careful backfilling to prevent tank damage.

Council approvals vary across Australia. Many councils allow tanks under certain sizes without permits, but underground rainwater tanks installations often trigger additional requirements. Always check with your local council before proceeding. Some heritage areas or flood-prone zones have specific restrictions.

Maintenance: What Does Each Tank Type Require?

Above-ground tanks need regular inspections for cracks, UV damage, and fitting integrity. Clean your gutters and first-flush diverters seasonally. Check screens for debris and inspect inlet and outlet connections annually. Sediment removal every few years keeps water quality high.

Underground rainwater tanks require pump maintenance and periodic professional inspections. Since you can't easily see the tank, scheduling regular checks matters even more. Inlet screens still need attention, and sediment accumulation requires occasional removal via access hatches.

Common issues include:

• Mosquito breeding (ensure all openings are properly screened)

• Algae growth (keep tanks dark and cool where possible)

• Sediment buildup (install first-flush diverters)

• Fitting failures (inspect connections regularly)

Choosing the Right Tank Size and Material

Popular materials include polyethylene (poly), concrete, and steel. Poly tanks offer affordability and versatility. Concrete provides excellent durability and naturally sweetens acidic rainwater. Steel tanks suit rural properties and offer great longevity.

Calculating your ideal capacity depends on roof catchment area, local rainfall patterns, and intended usage. A household using tank water for gardens and toilets might need 5,000 to 10,000 litres, while those seeking greater self-sufficiency could require 20,000 litres or more.

Material suitability varies by installation type. Poly works well for both applications. Concrete excels underground rainwater tanks due to its strength. Steel performs best above-ground where its durability and aesthetic appeal can shine.

Environmental Impact and Sustainability

Rainwater harvesting significantly reduces your environmental footprint. Every litre captured is one less drawn from stressed municipal supplies or natural waterways. During storms, your tank also reduces stormwater runoff, easing pressure on drainage systems.

Both tank types deliver identical water conservation benefits the environmental advantage lies in harvesting itself, not installation method. However, underground rainwater tanks may offer slight efficiency gains by keeping water cooler and reducing evaporation in hot climates.

Conclusion

Choosing between above-ground and underground rainwater tanks ultimately comes down to your specific circumstances. Above-ground tanks win on affordability, ease of installation, and maintenance accessibility. Underground rainwater tanks triumph when space is limited, aesthetics matter, or you're in a bushfire-prone area.