How do I fit a water butt to a downpipe?

A water butt is simple to fit and easy to get wrong in two ways: standing it on soft ground where it tips as it fills, and leaving the overflow to discharge against the house wall. A full 200 litre butt weighs 200kg, which is a lot of weight on a paving slab that was not levelled.

What you'll need

• A water butt with a tap and a lid
• A stand or blocks — high enough for a watering can
• A rainwater diverter kit for the downpipe size
• A hole saw and a fine saw
• A spirit level

Step by step

1. Choose a firm, level, accessible position.Next to a downpipe, on ground that will not settle. 200 litres of water is 200kg — a butt on soft soil or an unbedded slab will lean as it fills.
2. Build the stand high enough.The tap has to clear a watering can, which means around 400mm of clearance. A purpose-made stand, or bedded blocks and a slab. Check it is level in both directions with the butt empty.
3. Set the height of the diverter.The diverter must be at or slightly above the level of the top of the butt when it is on its stand. Water flows from the diverter into the butt by gravity, so the connection has to be higher than the water level.
4. Mark and cut the downpipe.Mark the diverter position on the downpipe. Most kits need a section cut out or a hole cut into the pipe — follow the kit instructions. Cut square with a fine saw and deburr.
5. Fit the diverter.Push-fit or clamp the diverter into the downpipe, then run the connecting hose to the butt, falling continuously towards the butt with no dips that can hold water and freeze.
6. Sort out the overflow.Most diverters stop diverting once the butt is full and let excess pass down the downpipe. Check yours does. If not, fit a separate overflow from the butt back to the downpipe or to a soakaway — never letting it discharge at the base of the wall.
7. Fit the tap and check for leaks.Most butts come with a bulkhead tap fitting with washers either side. Hand-tight plus a little, not over-tightened — the plastic splits.
8. Keep the lid on and secure.A lid keeps light out, which reduces algae, keeps leaves and debris out, and — most importantly — stops a child or an animal falling in. A secured lid is not optional in a garden used by children.
9. Plan for winter.Water expands as it freezes and can split a butt or the diverter. In a hard winter, drain the butt down and disconnect or divert the inlet.

Tips

• Link two butts with a connector kit at the bottom rather than buying one huge one. They fill and draw evenly and are easier to site.
• A first-flush or leaf filter in the diverter keeps the water much cleaner and reduces the sludge in the bottom.
• Do not use stored rainwater on edible seedlings or in a greenhouse without care — it can carry bacteria. Mains water is safer for those.

Common mistakes

• Standing the butt on soil or an unlevelled slab — It leans as it fills and can topple. 200 litres is 200kg and a falling butt is dangerous, particularly around children.
• Letting the overflow discharge at the base of the wall — It saturates the ground against the house, which causes damp and can undermine paving. The overflow must return to the downpipe or go to a soakaway.

If it doesn't work

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