Water Butts: Sizing, Siting and Linking Them Together

There is one fact worth getting straight before anything else in this series, because everything that follows depends on it.

Water you have collected and stored yourself is not covered by a hosepipe ban. The restrictions in force across much of England and Wales apply to water supplied through the mains. Rain that fell on your roof and went into a butt is yours to use as you like — with a can, with a hose, through an irrigation system, at any hour of the day. Every water company operating a Temporary Use Ban says so explicitly in its own notice.

That single fact is the difference between watching a border die and keeping it alive. So it is worth taking your water storage seriously, and most people's is an afterthought: one 100-litre butt on a downpipe, filled in April, empty by the second week of June.

How much you actually need

The arithmetic is more encouraging than people expect. A roof collects roughly 0.85 litres per square metre for every millimetre of rain that falls on it, once you allow for what splashes off and evaporates.

A modest house roof of 50 square metres, in a single 10mm shower — an unremarkable amount of rain, the sort that barely wets the path — will send about 425 litres down the downpipe. A shed roof of 6 square metres in the same shower gives you around 50 litres. A greenhouse, a garage, a lean-to: all of it is collection area you are currently sending into a drain.

The limit is almost never how much rain falls. It is how much you can catch and hold when it does. Miss a single autumn downpour because your butt was already full and you have lost more water than you will hand-carry in a fortnight.

As a rough working figure: 200 litres of storage per downpipe is a sensible minimum, and 400–600 litres is where you stop feeling anxious in a dry August. A 200-litre butt sounds like a lot until you realise a thorough soak of a single established shrub can take 20 litres.

Siting: four things that matter

Get it high enough. Water flows out of a butt under gravity alone, and a tap 15cm off the ground fills nothing but a saucer. Stand the butt on blocks, a purpose-made stand, or a stack of paving slabs so you can get a full-size can underneath. Aim for a tap height of at least 40cm. This is the single most common mistake and the one people regret every time they water.

Make sure the base is level and solid. Water weighs a kilogram a litre. A full 200-litre butt is 200kg standing on a small footprint. On soft ground, on uneven slabs, or on a stand that flexes, it will lean — slowly at first, then not slowly. Level, firm and boring is what you want.

Put it in the shade if you can. Warm, sunlit water grows algae and gets murky. A butt in shade stays cleaner for longer. It matters less than people think for watering ornamentals, but it makes the water considerably more pleasant to handle.

Keep the lid on. A sealed lid keeps out leaves, keeps out mosquito larvae, and — the serious one — keeps out small children and wildlife. An open butt is a drowning hazard and a hedgehog trap. If your lid is missing, replace it before you do anything else on this list.

Linking butts together

This is the upgrade that makes the biggest difference, and it is genuinely simple.

Two or more butts standing side by side can be joined near the base with a short linking kit — a length of hose and two tank connectors, sold as a set. Water finds its own level between them, so the pair fills and empties as one larger vessel. The overflow from the last butt in the chain goes back to the drain.

Three points people get wrong:

• Link low, not high. A connection near the base means both butts drain fully through your one tap. A connection near the top only shares the overflow, which is not the same thing at all and leaves half your storage stranded.
• Stand them at the same height. They must sit on the same level base, or the higher one will never empty below the level of the link.
• Keep the overflow honest. Whichever butt is last in the chain still needs a working overflow routed to the drain or to a soakaway, well away from the house wall. Linked butts fill fast in a downpour, and water going somewhere unplanned against a foundation is a much worse problem than the one you were solving.

If you are adding storage this year, adding a second butt to an existing downpipe is almost always easier and cheaper than plumbing a new downpipe, and doubles what you can hold.

One thing to be careful about

Fill your butt from the roof, not from the tap.

Topping a butt up with a hosepipe from the mains during a restriction is exactly the sort of thing that feels like a clever workaround and is not one. The rules follow the water, not the container. Mains water is mains water whether it goes into your border directly or sits in a plastic barrel for an hour first. Rainwater off the roof is a different thing entirely, and that is the water the exemption is about.

Where this goes next

Stored water is the foundation of every other tactic in this series. It is what makes a drip system legal everywhere regardless of who supplies your water, it is what keeps a newly planted tree alive through its first summer, and it is the only water you control.

If you are rethinking planting as well as watering, our drought and dry soil listings show plants that will handle a dry summer once they are established — and a garden that needs less water is the cheapest storage upgrade of all.

Get the butts in before the autumn rain arrives. That is when the tanks fill, and a butt bought in October catches a winter's worth of water for next summer.