Question answered
Fitting a water butt to a downpipe
The short answer
To fit a water butt, cut the downpipe at the height of the butt's inlet, fit a diverter, and run a short hose or pipe from the diverter to the butt. The diverter fills the butt, then lets the surplus carry on down the pipe. Always provide an overflow that leads away from the house, and stand the butt on a firm, level base.
A water butt is a simple job on most houses, but it moves rainwater around, and the details at the diverter and the overflow decide whether it helps your garden or quietly floods your wall.
How a downpipe diverter works
A diverter is a small fitting that replaces a short section of the downpipe. Water coming down from the gutter meets an angled opening, and a share of it turns into a side outlet leading to the butt. When the butt is full, the outlet closes or backs up, and the rest of the water drops down the pipe as it always did.
Some kits are designed for round pipe and some for square, and the sizes differ, so measure before you buy. Most are made to fit the common sizes of plastic downpipe. On cast iron or aluminium, the pipe has to be cut cleanly, and the diverter is often held with a clip or collar instead of being pushed on.
The idea is to let the butt fill from the first rain and then stay out of the way. If the diverter is fitted badly, the pipe can leak at the cut or throw water against the wall, so the seal and the alignment are worth taking time over.
Where to cut and where to stand the butt
Stand the butt first, then mark the pipe. The diverter should sit a little above the butt's inlet so the connecting hose falls downhill, and the pipe is cut at that level. Measure twice. A cut that is too low leaves no room for the fitting.
A full butt is heavy, because water weighs about a kilogram per litre. It needs a firm, level base such as a paved slab or a purpose-made stand, never loose soil or a wobbly block. Lifting the butt also improves the flow through the tap, so a stand often pays for itself.
Keep the butt clear of the wall footings and make sure any spill lands on ground that slopes away from the house. If the downpipe sits close to a boundary, think about where the overflow goes; it should not discharge onto a neighbour's side. Our guide to a shared gutter with a neighbour covers some of the practicalities of sharing drainage.
Why the overflow is the part that matters
On a quiet day a butt is easy to forget. In a storm it fills in minutes. If the diverter has no way to pass the rest of the flow, water backs up the pipe and out of the joints, or pours over the top of the butt against the wall.
A properly made diverter returns the surplus to the downpipe once the butt is full. A butt also needs its own overflow, a short pipe near the top that leads to a drain, a soakaway or the garden, away from the foundations. Fit a mesh over the inlet and a lid on the top so leaves stay out and children cannot fall in.
If the downpipe is partly blocked, the diverter makes the problem worse, as the water that cannot escape has nowhere to go. Our page on blocked downpipes explains how to spot one before you cut into the pipe.
Check the gutter and fascia before you add weight
A butt does not add load to the gutter, but a diverter changes how the downpipe behaves, and a gutter that already overflows will overflow more easily once a restriction is added. Before you fit one, run a hosepipe along the gutter and watch the outlet.
If the water spills over the front, or drips from the joints, put that right first. A leaking gutter next to a butt wastes the water you are trying to save, and a rotten fascia will not hold the brackets for long. See fascia capping over old timber for what to look for behind a gutter that appears sound from the ground.
It is also worth checking the pipe clips. A downpipe held by two or three tired brackets can bow once a diverter and a hose add weight at one point.
Keeping it working through the year
Butts need a little looking after. Empty and clean the filter in autumn so leaf mould does not block the inlet, and check the diverter flap or return for grit. In a cold spell, drain the connecting hose, because standing water that freezes can split a fitting.
Keep the lid on. A covered butt keeps the water clean and stops algae growing. The tap should sit well clear of the ground so a can slides under it, and a small tray beneath catches the drips.
For wider habits that keep a whole drainage system working, see our notes on roofline maintenance, or the main gutters, soffits and fascias page for the work we do on drainage and the roofline.
If you take the butt out for the winter, leave the diverter set so the water goes down the pipe, and put the fitting back in spring after checking the seal.
Butt and diverter: two questions before you cut
Is permission needed to fit a water butt?
If you own a house outright, a butt on an ordinary downpipe is a small job. A rented home, a flat with shared drainage or a listed building may have its own rules, so ask your landlord, freeholder or the Adur & Worthing planning team before you cut into an original pipe.
Will a water butt stop my gutter overflowing in a storm?
No. A butt fills quickly and then the downpipe has to carry everything else, as before. If your gutter overflows in heavy rain, the cause is more likely a blockage, a bad fall or a gutter undersized for the roof area, and a butt will not cure any of them.
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