Rainwater Harvesting in the Garden: Butts, Greywater and What Works

The Water Butt Exemption, and Why It Isn't a Loophole

It's worth restating plainly, because I still hear it described in hushed tones as though it's some clever way round the rules: a hosepipe run from a water butt, a tank, or any other stored or recycled water source is not restricted under the current ban. The restriction applies to water drawn through the mains, via your meter; once water is sitting in your own butt, it's simply no longer subject to the ban at all.

That matters practically, not just legally. It means the effort you put into rainwater harvesting pays you back directly during exactly the weeks when mains watering is off the table, which is why I'd always rather raise it with clients at the design stage of a garden than wait until a ban is already in force.

How Much Water a Roof Actually Collects

The arithmetic is worth doing in principle, even without pinning it to a specific figure, because it changes how people think about the size of tank or butt they actually need. The amount of water a roof collects comes down to the roof's area multiplied by the rainfall falling on it, minus a modest loss to evaporation, overshoot at the gutters, and the first flush of dirt off the tiles. Because a roof is such a large, flat collecting surface, even an ordinary shower across a typical Kent roof adds up to a genuinely significant volume, and spread across a whole year, that same roof would fill an average 200-litre butt many times over.

A single butt, drawn on daily through a hot spell, can be emptied within days. The shortfall in most Kent gardens is rarely rainfall; it's storage.

Why One Butt Is Never Enough

One butt, however well positioned, was never designed to carry a whole garden through a dry summer. Scaling up properly usually means a combination of these.

Linking Butts, Extra Downpipes and Overlooked Roofs

The simplest upgrade is linking two or three butts in series off the same downpipe, so the overflow from the first feeds straight into the next rather than running away down the drain. A second downpipe, where the roof allows it, effectively doubles your collecting area for very little extra plumbing.

The roofs people forget are usually the most useful: garages, sheds, greenhouses and outbuildings often have simple, uninterrupted pitches that are easier to fit a butt to than the main house, with nothing else competing for that water.

Larger Tanks, and Getting the Timing Right

Where a garden is being reworked anyway, this is the point to think about a proper tank rather than another butt: a slimline tank against a wall, or one sunk below a patio that's already being dug up. Sinking a tank once hard landscaping is finished means breaking up paving you've only just laid; doing it while the ground is already open costs a fraction as much. It's one of the cheapest decisions to get right at design stage, and one of the most expensive to retrofit.

Siting: Getting the Water Where You Need It

A butt only works well if gravity does some of the work for you. Raised on even a modest stand, it gains useful pressure at the tap, enough to fill a can quickly rather than dribble. Position matters as much as height: the closer a butt sits to the beds that need it most, the less carrying you do.

Butts are not attractive, and I say that as someone who spends most of his working life trying to make gardens look considered. Screening one behind planting, housing it in a built enclosure, or choosing a slimline model that tucks against a wall is far easier to arrange while a garden is being designed than after the fact.

Keeping Stored Water Usable

Stored water only stays useful if it's looked after. A butt needs a lid, both for safety around children and pets and to keep out light, which otherwise encourages algae to bloom inside; a dark or opaque butt does the same job by design. Mosquitoes will find any standing open water within days, so a properly fitted lid earns its keep several times over.

The overflow deserves more thought than it usually gets. I regularly find butts overflowing straight against a house wall, which over time becomes a damp problem rather than a drought solution. Route it somewhere sensible instead: into a second butt, a soakaway, or open ground well clear of the foundations.

Greywater, Honestly

Greywater is worth using during a hosepipe ban, and worth being honest about its limits. Cooled washing-up water and old bathwater are perfectly usable on established ornamental planting, tipped straight onto the soil around the base of the plant. The key word is quickly: use it the same day, because stored greywater goes septic and starts to smell within a day or two.

Avoid anything that's touched bleach, dishwasher salt, strong detergents or fabric softeners, and anything that's been in contact with nappies or food waste; these all build up in the soil or the water itself in ways plain water never would. Keep it off edibles and seedlings altogether. Greywater is a short-term drought measure you reach for during a dry fortnight, not a system you build a garden around.

Where Proper Systems Come In

Plumbed rainwater harvesting and greywater recycling systems do exist, feeding filtered, stored water back to outside taps or even indoors for flushing and laundry. They sit in a different order of cost and regulation to a butt and a watering can, and they're worth a conversation with a specialist if a garden or wider renovation is being planned from scratch. I'd rather a client understood that distinction honestly than assumed a butt in the corner was doing the same job.

Conclusion

The gardens that have come through this summer looking least stressed are, almost without exception, the ones where water was thought about properly when the garden was designed, not bolted on afterwards. A well-sized rainwater harvesting setup, alongside sensible, honest use of greywater in the short term, does more for a garden through a ban like this than most people expect from something so unglamorous. It's worth having that conversation at the design stage of your next garden, rather than in the middle of the next dry summer.