Why Rainwater Beats the Tap

Spring in the UK often arrives with a mix of warm sunshine and sharp showers, and dry spells can appear out of nowhere. A single hot weekend in April or May can leave pots, hanging baskets and newly planted seedlings gasping, just as everything is putting on growth. Rather than reaching for the hosepipe every evening, capture some of that free rain when it does fall.

Rainwater is not just free — it is better for plants than tap water. It is soft, slightly acidic and free from the chlorine that builds up in containers over time. Tomatoes, blueberries, camellias and rhododendrons in particular appreciate it. Storing it in a water butt also gives you a buffer against hosepipe bans, increasingly common in the south and east of England during dry summers. Setting up a simple collection system takes an afternoon, needs no specialist skills and costs very little.

Choosing and Siting Your Water Butt

Water butts come in sizes from 100 to 300 litres. For a typical suburban garden, a 200–250 litre butt is a sensible middle ground: large enough to make a real difference, small enough to tuck behind a shed or beside a wall. Linking two together doubles your storage for very little extra cost.

Place your butt where it will catch the most roof run-off. A downpipe from a garage, shed or house wall is ideal, as even a modest roof area can send hundreds of litres into the guttering during a decent shower.

• Height matters. Stand the butt on a solid, level base — a paving slab or plinth — so you can get a watering can under the tap. A full butt weighs around 200kg, so never balance it on loose soil or bricks.
• Check the overflow route. Position the butt so surplus water drains away from your house foundations, not towards them.
• Think about winter. Butts can crack if water freezes solid. Leaving the tap slightly open through hard frosts, or fitting an insulating jacket, avoids expensive surprises.
• Keep it accessible. A butt hidden behind a dense shrub will not get used. Put it somewhere you pass with a watering can every couple of days in summer.

Fitting a Diverter to the Downpipe

The clever bit is the diverter. Rather than cutting straight into the downpipe, a diverter sits inline and sends rainwater into the butt until it is full, then allows the rest to carry on down the drain. Two common types exist: a simple fit-and-forget unit that slots into a drilled hole, and a larger in-line version that requires cutting a section out.

Here is the straightforward approach:

• Mark the height on the downpipe that lines up with the top of your butt, leaving room for the connecting hose to run with a gentle downward slope.
• Drill a hole to match the diverter's collar, using a hole saw of the correct diameter. Take your time and support the pipe so it does not split.
• Fit the diverter body into the hole and seal it with the supplied gasket.
• Run the flexible hose to the butt's inlet, trimming it so there are no dips where water can pool. Secure it with the clips provided.
• Test with a watering can poured into the guttering above, or wait for the next shower. Water should trickle steadily into the butt with no leaks at the collar.

Connecting, Overflow and First Fills

If you are linking two butts, use a connector kit to join them near the base so they fill and draw down together. Fit the overflow pipe to the highest butt and direct it towards a soakaway, border or drain. This matters more than many gardeners realise: a full butt with nowhere for excess water to go will back up and spill around your foundations.

Once connected, the system fills itself. A single millimetre of rain on a 30 square metre roof yields roughly 30 litres, so even a modest shower tops up a butt quickly. Keep an eye on the first few fills to check the diverter is working.

Using Stored Water During Dry Spells

This is where the system earns its keep. In spring and early summer, prioritise the thirstiest plants: containers, hanging baskets, raised beds and anything newly planted. A mature shrub in open ground fends for itself far better than a tomato in a 10 litre pot.

• Water in the evening or early morning to cut evaporation losses.
• Water deeply and less often rather than little and often, which encourages shallow roots.
• Use a watering can with a rose for seedlings so you do not wash compost out of the pot.
• Group pots together in a shaded spot during hot spells to reduce demand.
• Mulch the surface of containers and beds with bark or gravel to lock in moisture.

Roughly 10 litres per week is enough for a well-mulched 30cm pot in average spring weather, rising to 20 litres in a heatwave.

Keeping the System Working

A little maintenance goes a long way. Each spring, empty and rinse the butt, clearing leaves and grit from the base. Check the diverter and hose for blockages, and clear moss from the guttering above so the water runs clean.

If algae becomes a problem, a purpose-made water butt treatment or a handful of barley straw keeps it in check without harming plants. Cover the butt with a lid to keep out debris and reduce mosquito breeding, and fit a child-proof lock if little ones are about.

With that small amount of care, a simple rainwater system will quietly supply your pots for years — and you will wonder why you ever did without it.