Rainwater tanks are growing in popularity among UK homeowners and self-builders as a way to live more sustainably and save on water bills. By capturing rainwater, you can reduce demand on mains water and help mitigate issues like droughts and storm runoff flooding. One key decision when planning a rainwater tank system is whether to install an aboveground tank or an underground tank. Both types of rainwater tanks can store water for uses such as garden irrigation, toilet flushing, or even laundry, but they come with different advantages and considerations.
What Are Aboveground Rainwater Tanks and How Do They Work?
Aboveground rainwater tanks are installed on the surface, in a garden or alongside a house, and are often the simplest way to start collecting and storing rainwater. Many homes already use small aboveground barrels or water butts connected to gutter downpipes to collect rain for watering plants. However, aboveground rainwater tanks can also be much larger, up to tens of thousands of litres, to serve bigger gardens, farms, or even some household uses. Here are the key pros and cons of aboveground rainwater tanks:
Advantages of Aboveground Rainwater Tanks
Lower Cost & Easy Installation
Aboveground rainwater tanks are generally cheaper to buy and install than underground ones. No digging or heavy machinery is required, and if you have a firm, level base, you can often set up an aboveground rainwater tank as a DIY project with basic tools. This makes them accessible for homeowners on a budget.
Simple Maintenance and Access
Because the tank is visible and not buried, it’s easy to inspect and clean. Any leaks or cracks can be spotted quickly and repaired without excavating. Routine maintenance (like cleaning out debris or checking filters) is straightforward when everything is above ground.
Flexible and Portable
Aboveground rainwater tanks can be relocated or expanded with relative ease. If you move home, you could even empty and take your tank with you, something not feasible with an underground tank. You can also link multiple aboveground rainwater tanks together to increase capacity if needed.
Great for Gardens (Hosepipe Ban-Friendly)
An aboveground rainwater tank is ideal for garden irrigation. During UK hosepipe bans or dry spells, you can still water your plants using stored rainwater and stay within the rules. Many aboveground designs allow gravity feeding with a tap or hose, so you might not need a powered pump for garden watering.
Variety of Sizes and Styles
There’s a wide range of aboveground rainwater tank designs, from slimline water butts that fit small patios to large vertical tanks for farms.
Drawbacks of Aboveground Rainwater Tanks
Exposure to Weather & Temperature Fluctuations
Because they sit outdoors, aboveground rainwater tanks are exposed to the elements year-round. In winter, water inside can freeze and expand, risking cracks in the tank if it’s not insulated. In summer, direct sun can heat the water. Without insulation or regular turnover, warm stagnant water can encourage algae or bacteria (such as Legionella) growth. It’s recommended to either insulate aboveground rainwater tanks or drain them during extreme cold, and to keep them shaded if possible.
Higher Maintenance Needs
Weather exposure means aboveground rainwater tanks may need more frequent maintenance. UV light can degrade some tank materials over time, and debris or algae may accumulate faster. Regular checks and cleaning are needed to keep the water quality good. The good news is that maintenance is easier to perform, but it does require diligence.
Aesthetic and Space Impact
A large plastic tank isn’t the prettiest garden feature. Even when manufactured in neutral green or black to blend in, aboveground rainwater tanks can be an eyesore in a small garden. They also take up valuable outdoor space, which can be a problem on compact plots. You might end up installing screens or fencing to hide the tank, adding to the cost.
Vulnerability
Aboveground rainwater tanks are more susceptible to accidental damage, impacts, or even vandalism. A surface tank could be damaged by garden tools, severe weather, or tampering in remote areas. Any damage could lead to leaks, so you’ll want to position the tank safely and secure it if vandalism is a concern.
Limited Water Pressure
If you plan to use the water for anything beyond filling a watering can, for example feeding an irrigation system or supplying a toilet, you might need a pump. Aboveground rainwater tanks can provide gravity pressure for small uses, but since they’re at ground level, the water pressure may be low. Elevating the tank on a stand can improve gravity flow slightly, but pumps or booster kits are often needed for higher-pressure requirements.
What Are Underground Rainwater Tanks and Are They Worth It?
Underground rainwater tanks (also called below-ground or in-ground tanks) are installed beneath the surface, typically buried in the garden or under a driveway. These rainwater tanks store water out of sight below ground, with the water pumped up when needed for use. Underground rainwater tanks are common in more advanced setups, for example where the rainwater is plumbed into the house to flush toilets, supply washing machines, or feed garden taps. They range in size, often from around 1,000 litres up to 10,000+ litres for domestic systems. Here are the main pros and cons:
Advantages of Underground Rainwater Tanks
Space-Saving & Hidden Installation
Placing a rainwater tank underground frees up your aboveground space. This is ideal for small gardens or urban plots where a bulky tank would be in the way. You can build a patio, lawn, or even a driveway over a buried rainwater tank (many underground tanks are structurally designed to support vehicle or pedestrian weight). The entire system is also out of sight, keeping your landscaping looking neat.
Stable Water Temperature & Quality
Underground rainwater tanks provide natural insulation thanks to the surrounding soil. This keeps the water cool and at a relatively constant temperature year-round, with no worrying about freezing in winter or overheating in summer. The cool, dark environment also discourages algae and harmful bacteria growth, helping maintain better water quality over time. Many below-ground rainwater tanks still include filters and calmed inlets to further protect water quality.
Protection from Damage
Buried rainwater tanks are generally safe from weather damage, UV exposure, and accidents. There’s no risk of storm winds blowing the tank over, and the stored water is secure from vandals or animals. The installation is permanent and very robust if done correctly.
Larger Capacities for Home Use
Because they’re hidden, underground rainwater tanks can be quite large without impacting your garden’s appearance. This makes them well-suited for storing significant amounts of rainwater to supply the home (for laundry, toilet flushing, etc.) or to provide ample irrigation water. With a sufficiently sized underground rainwater tank and a pump, you could cut mains water use by 40–50% in a home. In fact, new UK sustainable building standards increasingly encourage underground rainwater tanks as part of reducing potable water demand.
Year-Round Usage & Integration
An underground rainwater tank can be fully integrated into your home’s plumbing with automated control. For instance, many setups include a mains water backup, and if the tank runs low, a valve switches to mains supply, ensuring toilets or appliances always have water. Being underground also means the rainwater tank is unlikely to require seasonal shutdown, as the water won’t freeze.
Drawbacks of Underground Rainwater Tanks
Higher Installation Cost & Complexity
The biggest downside of underground rainwater tanks is the installation effort. You’ll need to excavate a substantial hole, which often means hiring a digger or contractor. The tank itself tends to be more expensive and built to withstand soil pressure. There are also costs for proper base preparation, backfilling, and possibly adding a concrete surround or reinforcement depending on soil conditions. Overall, the upfront cost of an underground rainwater tank is significantly higher than an equivalent aboveground setup.
Professional Installation Often Required
Unlike a simple water butt, installing an underground rainwater tank is usually not a DIY job for the average homeowner. It involves technical steps like connecting inlet/outlet pipework, setting up a pump and filtration, and ensuring the tank won’t float or collapse when empty. Mistakes can be costly, so many people opt to have professionals design and install the system.
Maintenance and Access Challenges
While underground rainwater tanks need less frequent upkeep, when maintenance or repairs are needed it can be more complicated. Access is through a manhole cover, and working on the tank might require entering a confined space or digging if there’s an issue. Simple tasks like cleaning the tank interior or fixing a leak are harder than with an aboveground tank. Installing pre-filters and an accessible pump can help minimise how often you need to open the tank.
Soil and Site Constraints
Your ground conditions will determine if an underground rainwater tank is feasible. High groundwater or a water table close to the surface can cause a buried tank to float. Very rocky ground can complicate digging, and heavy clay soil can exert pressure on the tank, with some manufacturers warning that high clay content soil may not be suitable for their underground rainwater tanks. Always check site conditions beforehand.
Less Flexibility After Installation
Once installed, an underground rainwater tank is essentially permanent. You can’t easily move it if you redesign your garden or relocate. Changing its position or upgrading capacity later would require new excavation. This means careful upfront planning of the tank’s size and placement is essential.
Requires Pump and Power
To use the water from an underground rainwater tank, you will almost always need an electric pump to push the water up to where it’s needed. This adds a small ongoing energy cost and another component to maintain. Aboveground rainwater tanks, by comparison, can sometimes work via gravity alone for garden watering if elevated, though pumps are still used for any fed-in systems.
Which Rainwater Tank Is Right for Your UK Home?
Choosing between an aboveground and underground rainwater tank ultimately comes down to your priorities: budget, space, and how you intend to use the stored water. In summary, an aboveground rainwater tank is an affordable, easy starting point, great for garden irrigation and modest water storage needs, with the trade-off of being visible and somewhat exposed. An underground rainwater tank offers a hidden, higher-capacity solution better suited for serious water reuse (like supplying toilets or multiple household uses), at the cost of a more involved installation and higher upfront expense. Both types of rainwater tanks can dramatically reduce your mains water usage and help make your home more sustainable.
If you’re still unsure which rainwater tank is best for your project, consider reaching out for expert advice. Many UK rainwater tank specialists (including our team) can assess your site and water needs and recommend a suitable system. Whichever route you choose, you’ll be joining a growing number of eco-conscious homeowners tapping into the free resource that falls from the sky. By installing a rainwater tank, you’ll not only save money and reduce water consumption, you’ll also be doing your part to buffer against droughts and reduce runoff in heavy rains.
Ready to get started? A good first step is understanding how much rainwater storage your property actually needs. Our rainwater tank size calculator helps you estimate the ideal capacity based on your roof area, rainfall levels, and intended water usage, so you can make an informed decision from the outset. Once you know the right size, you’ll be better placed to choose a rainwater tank that captures and stores water efficiently, supports your household needs, and maximises long-term savings.
Posted by Callum Vallance-Poole, on November 28, 2025.