Why Rainwater Suits a Garden Better Than the Tap

If you have ever stood at the end of a hosepipe in July, watching the meter tick round while the beds sag, you already understand the appeal of a water butt. Rainwater is soft, free of the chlorine and lime that mains water carries, and — crucially — it is not subject to the sort of restrictions that arrive with a hosepipe ban. Most UK water companies permit the use of stored rainwater during a ban, because it has never passed through the mains supply, though it is always worth checking your supplier's wording before you rely on it.

There is a practical argument too. A modest 30 square metre section of roof will yield roughly 30 litres for every millimetre of rain that falls on it. Across a typical British year of 700 to 900 mm of rainfall, that is somewhere between 21,000 and 27,000 litres running down your downpipes and into the drains. Capturing even a fraction of it turns a nuisance into a resource.

Sizing and Siting Your Butts

The temptation is to buy one butt and consider the job done. In practice, a single 200-litre butt under a 20 square metre roof section fills after only about 10 mm of rain — a decent shower. Once it is full, everything else goes straight down the drain. The aim is to store enough to see you through a fortnight of dry weather.

• Rough rule of thumb: allow 50 litres of storage per square metre of roof feeding the butt, if your budget and space permit.
• Link butts together with a low-level connector kit so the second and third fill only after the first is full, doubling or tripling capacity without extra diverters.
• Site on level, firm ground. A full 200-litre butt weighs over 200 kg. A paved plinth or a bed of compacted hardcore keeps it stable and lifts the outlet, which helps gravity flow.
• Keep it shaded if you can. Cool, dark water stays fresher and grows less algae.

Round butts are cheaper; slimline square ones tuck neatly against a wall or behind a shed. If space is tight, a pair of 100-litre wall-mounted butts will still make a difference to a small plot.

Connecting to the Downpipe: Diverters and Filters

Do not simply cut the downpipe and let it pour into the top of the butt. You will lose most of the water in heavy rain and end up with a permanently sodden patch against the wall. Fit a rainwater diverter instead — a simple unit that slots into a cut section of downpipe and channels water into the butt. When the butt is full, the diverter automatically sends the flow back down the downpipe as normal.

Filtration matters more than most people expect. Gutter debris, moss, bird droppings and grit all end up in the butt otherwise, and that sludge clogs drip lines and smells unpleasant by August.

• Gutter guards or a length of mesh along the guttering stop the worst of the leaves before they ever reach the diverter.
• A coarse filter or leaf trap in the diverter or the butt inlet catches moss and grit.
• A fine mesh screen over the butt inlet keeps mosquitoes and midges from breeding in the water. This matters far more than people realise — standing water with an open lid becomes an insect nursery.
• A first-flush diverter, if you want cleaner water, discards the first few litres of each rainfall, which carry most of the roof grime.

Overflow, Linking and Winter Behaviour

Every butt needs a clear overflow path. The simplest is a length of pipe from the butt's overflow outlet to a soakaway, a planted border, or a second butt. What you must avoid is letting overflow discharge straight onto the base of your house wall, where it can undermine footings and cause damp problems over a wet winter.

In winter, most modern butts cope with frost, but the fittings are less resilient. Exposed standpipes, taps and thin plastic connectors can split. Two sensible precautions: leave a little air space at the top of the butt so ice has somewhere to expand, and lag or drain any exposed pipework before the first hard frost. If you have room, an overflow soakaway also prevents winter waterlogging in the border where the butt sits.

Getting Water from Butt to Bed

Gravity is your friend, but it is a modest one. A butt raised half a metre above the soil gives you roughly 0.05 bar of pressure — enough to run a soaker hose or a length of drip line slowly, but nowhere near enough for a sprinkler.

• Soaker hoses and gravity drip kits work well from a raised butt and deliver water slowly, right where roots need it.
• Watering cans remain the most reliable method for pots, containers and young transplants, and they give you control over how much each plant receives.
• A small submersible pump — battery or mains — transforms a butt into a usable pressure source for a hose, though you will want to keep the intake off the bottom to avoid drawing sludge.
• Water the soil, not the leaves. It reduces disease pressure and means less water is lost to evaporation.

Keeping the System Healthy Through the Season

Rainwater is not sterile, and stored water can harbour bacteria if it sits warm and open. Keep lids on, keep the mesh clean, and give butts a rinse and a scrub each spring before the growing season starts. If you use stored water on salad crops, a rinse in clean water before eating is a sensible habit.

Check the diverter and filter every few weeks in autumn, when leaf fall does its worst. Clear the gutter guard, empty the leaf trap, and confirm that the overflow still runs freely. Ten minutes of maintenance in October saves a great deal of frustration the following July — and a well-set-up butt, quietly filling every time the clouds break, is one of the small, satisfying pleasures of countryside living.