Suffolk’s average annual rainfall. The UK average is 1,163 mm, making East Anglia the driest region in the country. The Environment Agency classified East Anglia at ‘High’ drought risk for summer 2026, its highest category. In 2025, nearly 9 million people in England were under hosepipe bans at the peak of the dry spell.
Capturing rainfall is straightforward and legal with no restrictions in the UK. Even a single water butt connected to one downpipe can supply weeks of garden watering through the driest part of summer. Larger systems, and simple habits around mulching and watering technique, extend that further. This guide covers the whole picture: from a basic water butt to scaling up storage, reducing how much water you need in the first place, and the careful use of grey water when supplies run low.
How much water falls on your roof
The formula is simple: multiply your roof area in square metres by the annual rainfall in millimetres and by a collection efficiency factor of around 0.8 (to account for evaporation, overflow during heavy rain, and filter drainage). The result is litres. A typical terraced house with a 50 m² roof in Suffolk collects roughly:
50 × 600 × 0.8 = 24,000 litres per year.
A standard 200-litre water butt captures a small fraction of that total, which is why linking butts together or moving to larger tanks makes a significant difference. Even connecting a single butt to just one downpipe is a meaningful start; the water you do store will be the water that gets used in the garden rather than lost to the drain.
Why rainwater is better for your plants
As rainwater falls through the atmosphere it absorbs carbon dioxide, giving it a slightly acidic pH that most garden plants, and especially acid-loving crops like blueberries, prefer. UK mains water is treated and typically more alkaline, particularly in East Anglia where hard water is common. Over time, regularly watering with alkaline mains water can gradually shift soil pH upward and lock out nutrients that plants need.
Mains water also contains chlorine and chloramine added during treatment. These do not usually cause immediate harm, but rainwater is free of them, and that matters more for seedlings and container plants than for established beds. For indoor plants and propagation, the difference is more noticeable still.
Your first water butt
A standard water butt holds around 200 litres and connects to an existing downpipe using a diverter kit, which is a simple fitting that redirects flow from the pipe into the butt and routes any overflow back to the drain once the butt is full. Installation takes around an hour and requires only a hacksaw and a screwdriver.
- Choose a spot near a downpipe on flat, stable ground. The butt should sit no more than 50 cm from the pipe.
- Raise the butt on bricks or a purpose-made stand so there is enough space to fill a watering can from the tap. A butt sitting directly on the ground leaves no room beneath the tap outlet, and water pressure will be very low.
- Position in shade where possible. Direct sunlight warms the water and encourages algae growth, which will eventually block the tap and filter.
- Mark the downpipe at the correct height before cutting. The cut should sit about 3 cm below the top rim of the butt. If the cut is too low, water can only fill the butt to that height and the top section stays empty. If the cut is too high, the overflow cannot return to the downpipe and the butt will spill over the rim.
- Fit the diverter and run the hose into the butt inlet. The hose should run slightly downhill to prevent slow flow or blockages. Use the rubber seal if supplied.
- Fit a lid to keep wildlife out and prevent mosquito larvae breeding in standing water. Most butts come with one; check it sits securely.
- Check the inlet for moss and debris each spring. If your butt stops filling despite rain, a blocked inlet is the most common cause.
Linking butts and increasing capacity
Two butts linked together double your storage with minimal extra effort. The most reliable method is to connect them near the top using a proprietary linking kit, so the first butt fills completely before water flows into the second. Both butts must sit at the same height for this to work; uneven ground causes one butt to take all the water while the other remains empty.
It is also possible to connect two butts at the base using 22 mm tank connectors, which allows water to be drawn from a single tap rather than two. However, debris accumulates at the bottom of any butt over time and a base connection is more likely to block. Near-top connections are simpler to maintain.
A single 200-litre butt can be exhausted in a few days of watering during a dry July. Three or four linked butts, totalling 600–800 litres, provides a much more useful reserve. Where space and budget allow, this is worth prioritising before considering a move to larger tank systems.
If you are helping someone set up water storage: a single water butt and diverter kit can be installed in under an hour with basic tools. Most DIY and garden centres stock complete kits for under £40. Check which downpipes are accessible and whether the person has room to raise the butt on bricks or a stand; low ground clearance under the tap is the most common frustration once it is in use. If connecting a second butt, bring a linking kit on the same visit rather than returning.
Scaling up: IBC tanks
An IBC (intermediate bulk container) is a 1,000-litre plastic tank inside a steel cage, mounted on a pallet. They are the food and chemical industry’s standard reusable container, which means a large second-hand market exists. Food-grade reconditioned units are available from around £40–50 on Gumtree or Facebook Marketplace; new tanks cost considerably more but are less variable in condition.
An IBC offers five times the capacity of a standard water butt in roughly the same footprint as two butts side by side. They can be connected to a downpipe using the same diverter approach, or fed from an overflow pipe from a butt system. The main practical considerations:
- Buy food-grade only. IBCs that previously held chemical products are not safe for garden watering even after cleaning; the plastic can retain traces of the original contents. Look for containers marked UN31HA1 or food-grade HDPE and ask the seller what the previous contents were.
- UV exposure degrades the plastic of an uncoated IBC over several years. Either choose a tank with a UV-stabilised outer cage and inner liner, or paint the exterior or cover with shade cloth if it will sit in full sun.
- Access for filling a watering can from the bottom tap requires the IBC to be raised on blocks or a pallet stand, just as with a butt. Plan this before positioning it; a full IBC weighs over a tonne and cannot easily be moved.
- The standard outlet valve is 50 mm and will need an adapter to fit a garden hose or watering can connector.
Reducing how much water you need
Capturing more water and reducing how much you use are equally important. The two most effective things a gardener can do are mulching and improving watering technique.
Mulching
A 5–10 cm layer of organic mulch applied over bare soil in spring, before the ground dries out, can reduce watering frequency by up to two-thirds according to the RHS. Mulch shades the soil surface, slowing evaporation, and organic materials break down gradually to improve the soil’s own water-holding capacity over time.
Wood chip, leaf mould, garden compost, and spent mushroom compost all work well. Keep the mulch at least 5 cm away from plant stems to prevent rot, and top it up each spring as it breaks down. On no-dig beds, mulch replaces digging as the primary way of improving soil structure; applied consistently over several years, the soil beneath will hold moisture noticeably better than a dug bed.
Watering technique
Where and when you water matters as much as how much you use. Watering directly at the base of plants, rather than over foliage, puts the water where roots can reach it and avoids the leaf wetness that encourages fungal disease. Watering in the early morning or evening reduces surface evaporation significantly compared to watering in the middle of a hot day. A watering can directed at the root zone uses less water more effectively than a sprinkler, which loses a large proportion to evaporation before it reaches the soil.
Grey water: what is safe and what is not
Grey water is household wastewater from sources other than toilets: baths, showers, and sinks. The RHS confirms that grey water can be used in gardens, but with clear limits on how and where.
Safe sources: bath water, shower water, and kitchen sink rinse water (provided it does not contain bleach or disinfectant). Washing machine rinse-cycle water is also considered acceptable by the RHS, though main-wash water is not.
Not suitable: dishwasher water (high in detergent and salt), any water containing bleach, disinfectants, or strong cleaning products, and toilet water of any kind.
Storage: grey water must be used within 24 hours. Bacteria multiply rapidly in standing grey water, making it harmful to plants and to people if stored longer. Do not store it in sealed containers overnight.
Where not to use it: the RHS advises against using grey water on edible crops that are eaten without cooking, which includes salad leaves, radishes, spring onions, and strawberries. It is safe to use on ornamental plants, fruit trees, and crops where the edible part is cooked or peeled (courgettes, squash, potatoes). Always apply with a watering can directed at the soil, not a hose or sprinkler: household grease and fibres in grey water can block irrigation systems and coating leaves with it is unhygienic.
Grey water is most useful as a supplement during dry spells when stored rainwater is running low, not as a replacement for it. A household of two people produces roughly 100–150 litres of grey water per day from baths and showers alone, which is a meaningful contribution to garden watering during a prolonged dry period.
Further reading
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RHS – Collecting, storing and reusing water (rhs.org.uk/garden-jobs/water-collecting-storing-and-using)
Practical guidance on water butts, grey water use, and reducing water demand, including their joint research with Cranfield University on water-saving techniques. The RHS also has a separate detailed guide to grey water safety at rhs.org.uk/science/gardening-in-a-changing-world/water-use-in-gardens/using-grey-water. -
Waterwise – Water efficiency in the garden (waterwise.org.uk)
Waterwise is the UK’s leading water efficiency organisation. Their garden section covers efficient watering techniques, drought-tolerant planting, and guidance on water butts and storage systems. -
Environment Agency – Managing water in a drought (gov.uk)
The EA’s drought guidance explains how drought status is assessed in England, what restrictions apply at each level, and what householders and gardeners can do. Their drought outlook publications give up-to-date risk assessments by region. -
Met Office – UK regional climate (metoffice.gov.uk)
The Met Office publishes rainfall averages by region, including a detailed Eastern England climate summary. Useful for calculating your own likely collection volumes and understanding seasonal patterns in Suffolk.