Why rural gardens are worth plumbing for rain

Rural properties usually come with the two things rainwater harvesting needs most: plenty of roof and plenty of plants. Every square metre of roof collects roughly one litre of water for every millimetre of rain, so a 50 square metre outbuilding in an area receiving 700mm a year sheds around 35,000 litres annually. Allow for gutter splash, overflow and dry spells and you might realistically capture 25,000 litres — far more than most gardens can use, and enough to make a serious dent in mains consumption.

The trick is matching storage to demand. A single 200-litre butt will fill in a heavy shower and then waste everything that follows. Most rural gardens find 1,500 to 3,000 litres of total storage comfortably carries them through a dry fortnight, especially if watering is done carefully. If you also want to flush toilets or run a washing machine, plan for considerably more.

Water butts: getting the basics right

Butts are cheap, simple and endlessly stackable. A few practical points make them work far better:

• Link them in series. Connecting kits join butts at the base so they fill and empty as one body of water. Put the tap on the lowest butt and the inlet on the first.
• Raise them on a solid plinth. A 60cm platform made from paving slabs on compacted hardcore gives a decent watering-can height and a little gravity flow. Roughly speaking, one metre of head produces about 0.1 bar — enough to push water through a short hose, but not a sprinkler.
• Use a downpipe diverter. These fill the butt while leaving the downpipe intact; once the butt is full, water simply carries on down the drain. They also filter out the worst of the grit.
• Keep them out of full sun. Dark, cool butts grow far less algae than warm sunny ones, and shaded water stays fresher for plants.

Site butts close to where water is used — beside the greenhouse, at the corner of a veg patch, next to the potting shed. A butt twenty metres away rarely gets used.

Larger tanks and outbuilding storage

Once you outgrow butts, the options widen. A 1,000-litre intermediate bulk container, often available second-hand, is the workhorse of rural storage: compact, stackable and easy to fit with an outlet. Purpose-made above-ground tanks of 1,500 to 2,500 litres look neater against a wall, while slimline models slot into narrow gaps between buildings.

Underground tanks of 2,000 to 5,000 litres are the tidiest solution and keep water cool and algae-free, but they need excavation, a pump and a properly designed overflow. Whatever you choose, insist on two things: the tank must be completely light-tight, and it must have a clear overflow route to a drain, soakaway or rain garden rather than the base of a wall. Do check listed-building rules and any local planning requirements before installing anything substantial near the front of a period property.

Filtration and water quality

Rainwater off a roof is not clean. It carries moss, bird droppings, grit and whatever has collected on the tiles. A simple layered approach handles most of it:

• Gutter mesh or leaf guards to stop the worst debris entering the system at source.
• A first-flush diverter, which discards the first half-millimetre or so of rainfall — the dirtiest part — before water reaches the tank.
• A coarse filter at the inlet, plus a floating intake that draws water from just below the surface rather than from the sludge at the bottom.

For ordinary garden use, that is plenty. Household non-potable use — toilet flushing, outdoor taps, sometimes washing machines — needs a pump, a pressure vessel and strict backflow prevention. Pipework must be clearly labelled and never cross-connected to the mains supply, and you should notify your water supplier before plumbing rainwater into the house. Rainwater is not safe to drink or cook with without full treatment, and roof material matters: avoid collecting from old lead flashing or weathered asbestos cement.

Simple irrigation that makes stored water go further

Gravity soaker hose is the simplest win — lay it along a bed, connect it to a raised butt and let it weep slowly into the soil. Drip lines with pressure-compensating emitters work well on a pumped system, and a battery timer can water at dawn while you are still asleep. Buried clay pots, known as ollas, release water slowly at the roots and suit long dry spells beautifully.

Whatever system you choose, mulch beds with 5–8cm of bark, compost or straw. It cuts evaporation by a third or more. Water early in the morning or late in the evening, aim at roots rather than leaves, and group thirsty plants together so one line serves them all. Overhead sprinklers lose up to half their output to evaporation and drift — a poor use of harvested water.

Maintenance through the year

A rainwater system rewards a little routine. Clear gutters and check leaf guards each autumn once the leaves are down. Inspect first-flush diverters and inlet filters before winter. Empty and scrub butts every couple of years with plain water and a stiff brush — never bleach, which will harm your plants.

Keep lids firmly closed to stop mosquitoes breeding and to prevent birds and hedgehogs falling in; leave a rough stick in any open water as an escape route. In freezing weather, leave headspace in tanks so ice can expand, disconnect hoses and insulate outdoor taps. Finally, make sure overflows discharge somewhere useful — a rain garden, a soakaway or a boggy planting bed — rather than onto a neighbour's land or against your own foundations.