Can you fit a water butt to a downpipe?

A diverter is a short section of pipe with a side outlet. You cut a gap in the downpipe, push the diverter into place and run a flexible hose from its side to the butt. Water coming down the pipe is directed through the hose. Once the butt is full, the flow simply carries on down the pipe, so the diverter works as a simple automatic valve with nothing to wear out.

Some models include a filter basket to catch leaves, and a few have a lockable flap you can close in winter. Others are fitted into a rainwater downpipe fed from a roof, with a connection that clips onto round or square pipe. Check the profile of your downpipe before you buy, because a diverter made for round pipe will not seal on a square one. Our page on gutter profiles explains how to tell which you have.

Choose a downpipe that serves a decent area of roof, ideally the one beside the garden. A butt filled from a tiny porch roof will stay nearly empty, while a downpipe draining the main roof will fill after a modest shower.

The base matters because water is heavy. A full butt of a couple of hundred litres weighs as much as two adults, and it will tip on soft soil or a wobbly paving slab. Use a solid, level stand, built from concrete blocks or a purpose-made plinth, and raise it high enough to slide a watering can under the tap.

Keep it clear of the wall base where you can, because a splashy overflow soaking the foundations or a damp-proof course is the opposite of what you want. If the downpipe sits close to a boundary, check whether the pipe is shared with the neighbour. The shared gutter page explains why agreeing first matters.

A butt that fills during a storm must have somewhere to send the extra, and a good diverter does this by returning the flow to the downpipe. If you add a second butt, link them with a short hose near the top so the first spills into the second.

Do not let the butt overflow onto the ground by the house wall, because a persistently wet foundation is a slow problem you will not notice until damp shows indoors, and do not block the downpipe below the diverter with a poorly cut section. A small chip or a ragged cut can catch debris and make the pipe slower to clear. If a downpipe is already prone to blocking, sort that out first. Our page on a blocked downpipe tells you what to look for.

In winter, an unemptied butt can freeze and split. Letting some water out through the tap, or closing the diverter, avoids damage. Leaves, algae and the odd frog are all kept out by a lid, so a tight one is worth having. A lid also slows algae and stops children or animals falling in, so choose one that fits tightly.

Stored rainwater is soft and free of chlorine, which many plants prefer, and it is useful for borders, pots and the lawn in a dry spell. It is no replacement for a drinking supply, and it should not be used for filling paddling pools or washing food.

Roof water can pick up bird droppings, moss debris and fine dust, so a mesh at the top of the diverter or at the butt inlet is worthwhile. If your roof has lead flashing, the water is still suitable for the garden, though we would not use it for anything beyond that. Our lead pages cover whether lead roofing is safe in more detail.

Treat the butt as a small piece of garden equipment, emptied and scrubbed once a year, rather than a fixed water supply.

A few practical habits keep it working. Fit a tap high enough above the base to take a watering can, and a second, lower outlet if you want to drain it fully. Check the hose connection after the first heavy rain, because a loose clip is the usual cause of a puddle by the wall. In a dry spell, a butt that fills slowly may not repay the fitting, so site it on the roof area that actually collects the most water.

Fitting a diverter on a ground-floor downpipe is a job most people can do with a hacksaw and a tape measure. It becomes a roofer's job when the downpipe is high, the bracket fixings are loose, or the gutter feeding it is already leaking, since there is little point storing water from a gutter that spills before it reaches the pipe. A common cause is a gap where water slips behind the gutter, as our page on the gap between roof and gutter explains.

Gutters that overflow and downpipes that run slowly are best put right before fitting a butt, because a butt only collects what the roof drainage delivers, and a faulty gutter wastes a good share of it down the wall instead. A gutter cleaning guide helps with the routine side of that.

If you want the roof drainage checked before you plumb in a butt, our survey photographs the gutters and downpipes at survey, and the written quote follows. Repairs carry a 10-year workmanship guarantee in writing, and anything we replace leaves the site with us. For the full picture, see gutters, soffits and fascias.