Rainwater Tanks
Large Underground Rainwater Tanks in the UK – Products Arriving Soon
Underground rainwater tanks provide a discreet, high-capacity solution for long-term rainwater harvesting and water storage across the UK. Installed below ground level, they allow substantial volumes of water to be stored without affecting usable space or property aesthetics.
With increasing pressure on mains water supplies and growing interest in sustainable water management, underground storage systems provide a practical way to improve water resilience and support large-scale rainwater harvesting.
Unlike smaller above-ground water butts, underground tanks are engineered for significantly greater storage capacity and long-term structural performance. Installed below ground, they are protected from UV exposure and temperature fluctuation, helping maintain stable storage conditions throughout the year.
At Outdoor Outlet, our underground tanks are selected for strength, durability and long service life. Manufactured using heavy-duty roto-moulded polyethylene, these systems are designed to withstand ground pressure and typical UK soil conditions when installed according to manufacturer guidance.
Our range includes large-capacity tanks typically starting from 20,000 litres and extending to over 60,000 litres, suitable for demanding residential, agricultural and commercial applications.
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Why Choose an Underground Rainwater Tank?
Discreet Installation
All storage is hidden below ground, preserving garden layout and visual appeal.
Higher Capacity
Underground systems typically offer significantly greater storage than standard water butts, helping you maintain supply during extended dry periods.
Protected Storage Conditions
Below-ground positioning reduces UV degradation and temperature fluctuation, improving long-term durability.
Scalable Systems
Many underground tanks can be integrated with pumps, filtration units and irrigation systems for expanded functionality.
What Size Underground Tank Do You Need?
Choosing the right size depends on:
1 - Roof surface area
2 - Average rainfall in your region
3 - Intended usage (garden watering vs irrigation system)
4 - Available installation space
Larger properties with extensive roof coverage can collect thousands of litres annually. Proper sizing ensures you maximise storage without overspending on unused capacity.
Built for UK Ground Conditions
Underground tanks must withstand soil pressure, potential surface loading and seasonal ground movement. The systems we supply are selected for structural integrity and long-term outdoor use when installed according to manufacturer guidelines.
For drive-over or traffic-rated applications, ensure the tank specification matches the intended load requirements.