Rain barrels collect rainwater from the roof and store it for the garden, giving you free, soft water for dry weeks. A single barrel under a downpipe can collect hundreds of litres from one rainy day, and that water is better for plants than tap water: it is soft, free of chlorine, and at the temperature of the air rather than cold from the mains. Rain barrels are simple to set up, cheap to run, and useful in any garden — especially for pots, seedlings and beds near the house. This guide covers how rain barrels work, how to choose and install one, how to use the water, and how to keep the system safe and working.
The principle is simple: rain falls on the roof, runs into the gutters, flows down the downpipe, and is diverted into a barrel instead of running away to the drain. The barrel stores the water until you need it, and you draw it off through a tap at the bottom into a watering can, or connect it to a hose or a drip system. A standard barrel holds about 200 litres, and larger tanks hold far more. Even a small roof collects a surprising amount of water: a roof of 50 square metres collects about 50 litres from each millimetre of rain. That means a few rainy days can fill a barrel many times over, and a barrel empties fast in a dry summer — which is why many gardeners link two or more barrels together. If you are unsure about rainwater harvesting in your area, check your local extension service for local rules and advice.
Choosing a rain barrel
Choose a barrel made from food-grade plastic or wood, with a lid, a tap near the bottom, and an overflow outlet near the top. A lid is essential: it keeps out leaves, debris and mosquitoes, stops the water turning green with algae, and is a safety measure — an open barrel is a drowning hazard for small children and animals. The tap should be high enough to fit a watering can underneath, so the barrel needs to stand on a sturdy platform of bricks or blocks, at least 30 cm high. The overflow should lead back to the drain or to a second barrel, so the barrel does not flood the house wall when it is full. A diverter — a fitting that sits in the downpipe and channels water into the barrel, then lets excess water flow down the pipe when the barrel is full — is the best way to connect a barrel, because it prevents overflow and can be closed in winter. Wooden barrels look attractive but need more maintenance; plastic barrels are lighter, cheaper and longer-lasting. Avoid barrels that once held chemicals, and check that any second-hand barrel is food-grade.
Installation step by step
Start by choosing a downpipe near the garden, on level ground where the barrel will not flood the house. Build a level, sturdy platform of bricks, blocks or a concrete slab, high enough to fit a watering can under the tap. Place the barrel on the platform and check it is level and stable — a full 200-litre barrel weighs about 200 kilograms, so the platform must be solid. Fit the diverter into the downpipe at the height of the barrel's inlet, following the manufacturer's instructions, and connect the diverter hose to the barrel. Fit the overflow hose and lead it to a drain, a soakaway or a second barrel. Fit the tap if it is not already fitted, and check all joints for leaks. Wait for rain, and check that the barrel fills, the overflow works, and nothing leaks. If you link two barrels, connect them with a hose near the top so water flows from the first to the second when the first is full, and draw water from the second barrel's tap. Keep the barrel out of direct sun where possible, or cover it, to slow algae growth.
Using rainwater in the garden
Rainwater is excellent for almost all garden uses. Use it for pots and containers, which dry out fast and need frequent watering; for seedlings, which are sensitive to cold tap water and chlorine; and for beds, through a watering can or a drip system. It is especially good for acid-loving plants, because it is naturally soft and slightly acidic, while tap water in hard-water areas is alkaline and can raise soil pH over time. Do not use rainwater from a roof with lead flashing or old lead paint for edible crops, and do not use water collected from a roof treated with moss killer or other chemicals until the roof has been washed by several rains. Use rainwater promptly rather than storing it for months, because stored water can go stale and breed mosquitoes if the barrel is not covered. Our watering systems guide compares watering methods, and drip irrigation explains how to connect a barrel to a drip system — a raised barrel often gives enough pressure, though a filter is important.
Maintenance and safety
Rain barrels need a little maintenance to stay safe and working. Clean the barrel out once a year, in late winter before the growing season: empty it, scrub the inside with a brush and clean water, and rinse it out. Do not use bleach or strong chemicals inside a barrel used for edible crops. Clean the gutters and the diverter filter regularly, because leaves and debris block them and stop the barrel filling. Keep the lid on at all times, and fit a fine mesh over the inlet and overflow to keep mosquitoes out. Check the platform and the barrel for stability, and check joints for leaks. In cold climates, empty the barrel or leave the tap open in winter so frozen water does not crack it. Keep children safe: a barrel with a secure lid is essential, and never leave an open barrel where small children can reach it. Wash produce before eating, as you should with any garden water, and see our garden safety guide for more on garden hygiene. If you are unsure about local rules on rainwater harvesting, check your local extension service.
Common mistakes
The most common mistake is no lid, so the barrel breeds mosquitoes, fills with leaves and turns green with algae. The second is no overflow, so the barrel floods the house wall when it is full. The third is a barrel sitting on the ground with the tap too low to fit a watering can underneath — raise it on a platform. The fourth is a barrel on an unstable platform, which can topple when full. The fifth is using a barrel that once held chemicals. The sixth is never cleaning the barrel or the gutters, so the water goes stale and the barrel stops filling. And the seventh is expecting one barrel to water a whole garden through a dry summer — a barrel is a useful supplement, not a complete water supply, so link barrels or use it alongside mains water.
Frequently asked questions
How much water does a rain barrel collect?
A roof of 50 square metres collects about 50 litres from each millimetre of rain, so a single rainy day can fill a 200-litre barrel. How much you collect depends on roof size, rainfall and how well the gutters and diverter work.
Is rainwater safe for vegetables?
Yes, in most cases. Rainwater from an ordinary roof is safe for watering vegetables, provided the roof has no lead flashing or old lead paint and has not been treated with chemicals. Always wash produce before eating, as you should with any garden water.
Do rain barrels breed mosquitoes?
They can, if the barrel is open or the lid is loose. Keep the lid on at all times, fit fine mesh over the inlet and overflow, and use the water regularly so it does not stand for months. A covered barrel with mesh is not a mosquito problem.
Can I connect a rain barrel to drip irrigation?
Yes, if the barrel is raised enough to give pressure, or with a small pump. Drip systems need low pressure, so a raised barrel often works, but a filter is important because rainwater carries debris. Our drip irrigation guide explains the setup.
Should I empty my rain barrel in winter?
In cold climates, yes — empty it or leave the tap open so frozen water does not crack the barrel. In mild, frost-free climates, you can leave it full. Check your local extension service for advice on winter care in your area.