Rainwater tanks are containers that collect and store rainwater, usually from a roof, for outdoor uses such as watering plants and lawns. They can reduce reliance on mains water, lower water bills, and ease pressure on drainage systems during heavy rain. This guide explains the main types of rainwater tanks, how to choose the right size, where to place one, how to install and maintain it, and how to use the stored water safely in your garden.
What Are Rainwater Tanks?
A rainwater tank is a storage vessel connected to a downpipe or collection system. When it rains, water flows from the roof into the tank instead of running into drains. The water is typically used for non-drinking purposes, such as garden watering, lawn care, and outdoor cleaning. For garden use, rainwater is often suitable as-is, but it should not be assumed safe for drinking without proper treatment.
Tanks come in many shapes and sizes, from small barrels to large underground cisterns. The right choice depends on how much water you want to store, the space you have, and how you plan to use the water.
Types of Rainwater Tanks
Above-Ground Tanks
Above-ground tanks are the most common and easiest to install. They sit on a level base beside a building or fence and connect directly to a downpipe. Because they are visible and accessible, they are simple to inspect, clean, and repair. They are available in materials such as plastic, metal, fiberglass, and concrete.
Below-Ground Tanks
Below-ground tanks are buried and can save space above ground. They keep stored water cooler and are less visible, but installation is more involved and usually more expensive. A pump is often needed to move water from an underground tank to the garden.
Slimline and Space-Saving Tanks
Narrow tanks are designed for tight spaces such as the side of a house or a narrow garden path. They may be tall and thin or flexible bladder-style tanks that fit into awkward areas. These are useful when space is limited but still require a stable, level base.
Common Tank Materials
- Plastic: Lightweight, affordable, and resistant to rust. Look for UV-resistant designs if the tank will be in direct sunlight.
- Metal: Durable and long-lasting, but may need a protective liner and checks for corrosion.
- Concrete: Strong and stable, with good temperature control, but heavy and difficult to move.
- Fiberglass: Lightweight and corrosion-resistant, though generally more expensive than plastic.
Choosing the Right Size
There is no single correct size for every garden. Consider three main factors:
- Roof area: A larger roof collects more water. As a rough guide, about 0.6 gallons of water can be collected per square foot of roof for every inch of rain.
- Local rainfall: Areas with frequent rain may need less storage to capture useful amounts, while drier areas may benefit from larger tanks to carry water through dry spells.
- Garden needs: Small gardens may only need a few hundred gallons, while larger gardens with many plants may need 1,000 gallons or more.
Also think about available space, budget, and whether the tank will be above or below ground. A tank that is too small will overflow often, while one that is too large may be expensive and unnecessary.
Where to Place a Rainwater Tank
Place the tank on a firm, level surface that can support the weight of a full tank. Water is heavy, so a weak base can cause the tank to lean or crack. Position it close to a downpipe to keep pipework simple and efficient.
If possible, place the tank slightly uphill from the garden or on a stand so gravity can help move water. Keep the tank away from areas prone to flooding and make sure overflow water is directed away from building foundations. Leave enough space for access, inspection, and maintenance.
How to Install a Rainwater Tank
- Plan and check rules: Confirm any local requirements for tank placement, size, or permits before you buy.
- Prepare a level base: Use a solid, level material such as concrete, compacted gravel, or a purpose-built base.
- Position the tank: Place it near the downpipe and on the prepared base.
- Connect the inlet: Direct roof water into the tank through a suitable inlet. A leaf screen helps keep debris out.
- Add a first-flush diverter: This device sends the first dirty water away from the tank so cleaner water is stored.
- Install an overflow: Make sure excess water can escape safely and is directed away from buildings.
- Fit an outlet or tap: Connect a garden hose, drip irrigation line, or pump as needed.
- Secure and test: Check that the tank is stable, all connections are tight, and water flows correctly.
For safety, secure the tank against tipping and keep lids firmly closed. If children have access to the area, make sure the tank cannot be climbed into.
Maintaining Rainwater Tanks
Regular maintenance keeps water cleaner and extends the life of the tank:
- Inspect the tank, pipes, and screens several times a year.
- Clean gutters and leaf screens so water can flow freely.
- Check for leaks, cracks, and loose fittings.
- Keep the lid sealed to prevent mosquitoes from breeding and debris from entering.
- Remove sediment if it builds up at the bottom of the tank.
- Drain and clean the tank occasionally, following the manufacturer’s guidance.
In cold climates, drain above-ground tanks or protect them from freezing if they are not designed for winter use.
Using Stored Water in the Garden
Stored rainwater can be used for most garden watering. A simple tap and watering can work for small gardens, while a pump or gravity-fed drip system is better for larger areas. Water early in the morning or evening to reduce evaporation.
Rainwater is generally suitable for lawns, ornamental plants, and outdoor cleaning. For edible plants, wash produce before eating. If you plan to use rainwater for drinking or food preparation, it must be treated and tested appropriately.
Benefits and Limitations
Rainwater tanks can reduce mains water use, capture free water for the garden, and help manage stormwater runoff. They can also provide a water source during restrictions or dry periods. However, tanks have an upfront cost, take up space, and require regular maintenance. Storage is limited by rainfall, and stored water is not automatically safe for drinking.
Conclusion
Rainwater tanks are a straightforward way to collect and store garden water. Choose a tank type and size that match your roof area, rainfall, garden needs, and available space. Install it on a stable base with proper inlet, overflow, and screening, then maintain it regularly. Used correctly, a rainwater tank can make garden watering more efficient and help you make the most of every rainfall.
For more practical guides on home and garden topics, explore the helpful articles on our site.