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For anyone managing a rural smallholding, a decent rainwater collection system is one of the simplest and most rewarding improvements you can make. It saves mains water, reduces runoff around buildings, and gives you a ready supply for beds when the dry spells hit. Building one is straightforward, but a few thoughtful details make all the difference.

Why Harvest Rainwater on a Smallholding?

Mains water is treated to drinking standards, so using it on the garden is wasteful. Rainwater is soft, free from chlorine, and at the right temperature for plants. It also costs nothing once the system is in place.

During a dry spell, a hosepipe ban can leave your beds gasping, but stored rainwater is usually exempt. A typical UK roof of 100 square metres can capture around 80,000 litres over a year. You will not store all of that, but you can make a serious dent in your watering needs.

Capturing rain also reduces runoff around foundations, which helps prevent damp and erosion. On a smallholding, with outbuildings and polytunnels, the potential is enormous.

Choosing and Siting Your Water Butts

Water butts come in many shapes and sizes. Start with at least two 200-litre butts linked together. Linking kits connect them with a short pipe near the top. The first butt fills, then the overflow runs into the second. A 1,000-litre tank is better if you have space, but it needs a firm, level base.

Position matters. Put your butts near a downpipe that collects from a decent roof area, but not so close that they block a path. Raise them on a sturdy stand, because every metre of height gives about 0.1 bar of pressure. That is enough to run a soaker hose over a short distance, or to fill a watering can without bending double.

• Stability: A full 200-litre butt weighs over 200 kg, so use a proper stand or a paved base.
• Overflow: Fit an overflow pipe that directs excess water to a soakaway, a pond, or a nearby bed. Never let it run against a wall.
• Access: Leave room to get a watering can under the tap and to reach the lid for cleaning.

Connecting Downpipes and Fitting Leaf Guards

The heart of the system is the connection between your downpipe and the butt. Cut a section out of the downpipe and fit a rainwater diverter. The best ones include a leaf guard and a first-flush option. A first-flush diverter sends the first few litres of rain, which carry the most bird droppings and moss, to waste before cleaner water enters the butt.

If you prefer a simpler approach, fit a leaf guard basket or a fine mesh screen at the inlet of the butt. This catches leaves, twigs, and moss. Check it after every storm, especially in autumn. A blocked leaf guard means water overflowing at the downpipe and none in your butt.

Do not forget mosquito mesh over any open vents or inlets. Standing water can become a breeding ground for insects. A piece of fine netting secured with a bungee cord works well.

When you cut the downpipe, measure twice and cut once. Fit the diverter according to the instructions, and make sure the pipe from the diverter to the butt has a gentle fall. Secure every joint. A leaky connection wastes water and can stain walls.

Managing Your System Through the Year

A rainwater system is not fit-and-forget, but it is not demanding either. A few seasonal checks keep it working well.

• Spring: Clean out gutters and leaf guards. Check taps, washers, and overflow pipes. Rinse the inside of the butts if they look grimy.
• Summer: Monitor levels during dry spells. Water early in the morning or late in the evening. Prioritise newly planted trees, vegetables, and greenhouse crops.
• Autumn: This is the busiest time for leaf guards. Check them weekly. If you have a first-flush diverter, empty and clean it.
• Winter: Make sure overflows are clear and not frozen. If a hard frost is forecast, leave some air space in the butt to allow for expansion.

Every few years, drain a butt and scrub the inside with a stiff brush and plain water. Avoid harsh chemicals, as residues can harm plants. If you have algae, a dilute solution of vinegar and water will help, but rinse thoroughly afterwards.

Using Stored Water in the Garden

When the dry spell arrives, get that water to the roots with minimal waste. A watering can is the simplest tool, and it lets you target individual plants. For larger beds, a gravity-fed soaker hose is excellent. Connect it to the butt tap and lay it along the row. With the butt raised a metre, you will get a slow, steady soak over a run of 10 to 15 metres.

If you need more pressure, a small submersible pump can push water through a drip irrigation line. That is more complex, but it is a good option for a large vegetable patch or a polytunnel.

Whatever method you use, mulch after watering. A layer of straw, compost, or woodchip slows evaporation and keeps the soil cool. Water in the evening or early morning, and give beds a good soak rather than a daily sprinkle. A full 200-litre butt will deliver about 10 mm of water over 20 square metres, which is a decent weekly drink for most vegetables in summer.

Finally, keep a rain gauge near your butts. It helps you understand how much you are capturing and when you might need to ration. After a few seasons, you will develop a feel for it. There is a quiet satisfaction in watching a summer storm fill your butts, knowing that your beds will be fine for another week.