Connecting a Rain Barrel: Harvesting Rainwater from the Downpipe
Install a rain diverter with overflow stop in the downpipe – free watering supply in two hours
Disclaimer
This guide has been prepared with great care. Nevertheless, we accept no warranty for the accuracy, completeness or currency of its contents. You follow this guide at your own risk – any liability for personal injury, property damage or financial loss arising in connection with its use is excluded. The contents do not replace professional advice for your individual situation. Always observe the manufacturer instructions of your tools and materials as well as applicable local regulations (e.g. building codes, neighbour law, utility line enquiries before digging). Work on electrical, gas or water lines and on load-bearing structures must only be carried out by qualified professionals.
Install a rain diverter with overflow stop in the downpipe – free watering supply in two hours
Rainwater is the best and cheapest watering supply: soft, lime-free and at garden temperature. One square metre of roof delivers several hundred litres of it per year – water that otherwise runs unused into the sewer. The most convenient route into the barrel is a rain diverter, also called a filler unit: it is installed in the downpipe, feeds part of the water through a hose into the barrel and stops the supply automatically as soon as the barrel is full. Installation only requires one confident cut into the downpipe – we show how to get it right and what matters when it comes to location and mounting height.
Tools
- Drill with hole saw (diameter per the diverter instructions)
- Hacksaw or pipe cutter
- Spirit level
- Folding rule and pen
- File or sandpaper for deburring
Materials
- Rain diverter / filler unit with overflow stop matching the downpipe diameter
- Rain barrel with a child-safe, lockable lid
- Connection hose with seals (usually included with the diverter)
- Paving slabs or concrete slabs for the base
- Barrel stand for comfortable watering-can access if needed
Step by Step
Choose the location and prepare the base
The barrel stands right next to the downpipe on a level, load-bearing base. Bear the weight in mind: a full 300-litre barrel weighs a good 300 kg – soft ground gives way, and the barrel tips over or tears out the connection. Compacted grit topped with paving slabs has proven itself. A sturdy stand brings the tap up to watering-can height.
Determine and mark the mounting height
The rain diverter is mounted at the height of the desired maximum water level – usually just below the rim of the barrel. The overflow stop works on the principle of communicating vessels: once the water in the barrel rises to the height of the diverter, no more flows in and the rest drains down the downpipe. If the diverter sits too high, the barrel overflows. Transfer the height from the barrel to the downpipe with a spirit level.
Drill or cut into the downpipe
Depending on the diverter model, drill a round hole into the downpipe with the hole saw or cut out a section of pipe – follow your diverter’s installation instructions exactly. Plastic pipes are easy to saw; on zinc downpipes, work with a hacksaw and gloves. Deburr the cut edges carefully.
Insert the rain diverter
Fit the diverter into the downpipe as instructed and point the hose outlet towards the barrel. Most models have an integrated filter that returns leaves and coarse dirt to the downpipe – keep it accessible so you can clean it once or twice a year.
Connect the barrel
Using the hole saw, drill the connection hole into the barrel wall – at the same height as the diverter – and fit the hose connector with the supplied seals. The connecting hose should run as short and horizontal as possible; a sagging hose slows the inflow. Then put on the lid and lock it.
Test run and winter care
Check the connection for leaks during the next rain, or pour a bucket of water into the downpipe. Before the first frost, drain the barrel completely, leave the tap open and switch the diverter to winter mode or remove the hose – otherwise freezing water will crack the barrel, hose or diverter.
At a Glance
Safety First
- Take child safety seriously: an open rain barrel is a drowning hazard for small children. Only use barrels with a firmly lockable, child-safe lid – and close it even during short watering breaks.
- Ensure a stable, level and load-bearing base: 300 kg of tipping weight is no toy, especially when children handle or climb on the barrel.
- Sawing zinc downpipes creates sharp edges – wear gloves and deburr the edges. For work above comfortable reach, use a sturdy ladder on firm ground.
- Collected rainwater is for watering, not drinking – and should not be used to fill paddling pools either.
Mistakes You Should Avoid
Mounting the diverter too high on the downpipe
If the rain diverter sits above the rim of the barrel, the overflow stop only kicks in long after the barrel has overflowed – and the water finds its way along the house wall. The diverter height determines the maximum fill level, so: transfer the height from the barrel to the pipe, not the other way round.
Placing the barrel on soft or uneven ground
On bare garden soil, the full barrel sinks in on one side, tips over or pulls the connection hose out of the diverter. A few paving slabs on compacted ground cost little and carry the load permanently.
Not draining the barrel in winter
Freezing water expands and reliably cracks plastic barrels, taps and diverters. Drain completely before the first frost, leave the tap open and turn the diverter to its winter setting – five minutes of effort that save you a new purchase in spring.
Common Questions
At what height is the rain diverter mounted?
At the height of the desired maximum water level in the barrel, i.e. just below its rim. As soon as the water level in the barrel reaches this height, no more water flows in – that is the principle of the overflow stop. If the diverter sits higher, the barrel overflows.
Can a rain barrel with a filler unit overflow?
Not if the mounting height is chosen correctly: the overflow stop automatically returns excess water down the downpipe as soon as the barrel is full. The prerequisites are that the diverter does not sit above the barrel rim and that the connecting hose is unobstructed.
What does connecting a rain barrel cost?
A rain diverter with overflow stop costs about €15–50 depending on the model, a 300-litre barrel with lid €40–80, plus fittings and slabs for the base. In total you usually end up at €60–150 – the investment pays for itself through saved tap water within a few years.
Do I have to empty the rain barrel in winter?
Yes, definitely. Freezing water cracks the barrel, tap and diverter. Drain the barrel completely before the first frost, leave the tap open and switch the rain diverter to winter mode so all the water runs down the downpipe again.
How much rainwater comes off the roof?
As a rule of thumb, one square metre of roof delivers about 500–800 litres per year, depending on regional rainfall. A downpipe draining 50 m² of roof easily fills a 300-litre barrel in one good summer downpour – frequent waterers benefit from a second barrel or, better still, a cistern.
When is a professional worth it?
A rain barrel is the easiest entry into rainwater harvesting – if you want more, you quickly reach its limits: for irrigating larger gardens, an underground cistern holding several thousand litres pays off, and if rainwater should soak away on your property or water backs up in the basement during heavy rain, professional drainage planning is called for. That is exactly what we do: drainage systems, soakaways, cisterns including earthworks and connecting pipes – from planning to installation with our own excavator. That way, the rain from your roof becomes a well-thought-out system instead of a wet surprise.
