Why bother harvesting rain on a smallholding

If you keep livestock, run a polytunnel and water a decent-sized veg plot, you will already know how quickly a hosepipe empties a water butt. Mains water is expensive, chlorinated and, in a hot July, sometimes restricted exactly when you need it most. Rainwater is soft, free at the point of use and far kinder to acid-loving plants such as blueberries, rhododendrons and camellias.

The maths is encouraging. Every square metre of roof catches roughly one litre of water for every millimetre of rain. A modest 60 square metre barn roof in a 700mm rainfall area could theoretically yield around 42,000 litres a year. Even allowing for evaporation, overflow and the rain you miss while a tank is full, capturing half of that is a serious saving.

Do the sums before you buy tanks

Work backwards from use, not from the size of the roof. Add up what you actually draw in a dry week:

• A hanging basket or large container: 5–10 litres a day in high summer.
• A 6m x 3m polytunnel: 100–200 litres a week, more in a heatwave.
• Ten hens: roughly 3–5 litres a day.
• A few sheep: 4–6 litres each per day.
• A horse or a couple of pigs: 30–50 litres each per day.

If that lot comes to 250 litres a day, a fortnight of dry weather needs 3,500 litres of storage. That is two 1,000-litre IBCs plus a cluster of butts, which is realistic for most smallholdings. Install more than you think you need if you plan to irrigate a field trough — you will never regret the extra capacity, and tanks can be linked together with simple overflow pipes.

Catching it clean: gutters, guards and first flush

The quality of what you store depends almost entirely on the first few metres of the system. Start with the roof itself: tiled, slate and modern coated metal roofs are all fine. Avoid collecting from old asbestos cement sheets, felt roofs in poor condition, or anywhere with lead flashing if the water is destined for edible crops.

Fit a gutter guard or mesh leaf trap at the top of each downpipe, then a downpipe diverter that sends the first flush of dirty water to waste. A basic first-flush chamber holding 10–20 litres is plenty; it captures the dust, bird droppings and moss that arrive with the first minutes of rain. After that, a fine stainless or nylon strainer of around 0.5mm, checked and rinsed every month through autumn, will keep most debris out of the tank.

Tanks, taps and getting water moving

Water weighs one kilogram per litre, so a 1,000-litre IBC on a wobbly pallet is an accident waiting to happen. Build a firm, level base of paving slabs or a concrete pad, and never stack butts on stacked pallets. Dark, opaque tanks keep algae at bay; if you use translucent butts, paint them or wrap them in black polythene.

Gravity is the cheapest pump you will ever own. Every metre of head between the tank outlet and the tap gives roughly 0.1 bar of pressure, which is enough for a hose or a drip line but not for a sprinkler. If you need more, a small submersible or inline booster pump will do the job. Whatever you install, fit a tap or two at convenient heights, add an overflow pipe that runs to a soakaway, pond or flower bed rather than flooding the yard, and place a childproof lid on every tank.

Using rainwater for crops and livestock

For plants, rainwater is close to ideal — no chlorine, no limescale, and a pH that suits ericaceous subjects. Use it on the veg plot, in the greenhouse, for seedlings and for topping up ponds. Water at the roots in the early morning or evening to cut losses to evaporation.

For livestock, the rules tighten. Stored water should be kept cool, dark and covered, and drawn from a tap rather than dipped out with a bucket that has been in a muck heap. Clean the troughs weekly and flush the lines occasionally. Well-maintained rainwater is perfectly suitable for hens, sheep, pigs and horses, but if you are unsure about the condition of your roof or tank, have the water tested before making it the sole supply for drinking.

Winter care, safety and a yearly routine

Frost is the enemy of pipework, not usually the tank itself. Insulate exposed pipes and taps, and either drain down the system or leave tanks part-full with room for ice to expand. Fit an escape ramp — a sturdy piece of timber or a rope — in every open trough so that hedgehogs and small birds can climb out. Keep children away from open water and secure all lids.

Once a year, in late autumn, empty and scrub each tank, clear the gutters, replace or clean the filters and check the first-flush chamber. It is an hour's work that pays you back in cleaner water, fewer blockages and a system that quietly fills itself every time the sky turns grey.