Rainwater harvesting

Rainwater harvesting: the best tips for your garden


In the summer months when the weather’s at its driest, your garden can be crying out for water. Rainwater harvesting provides an alternative to reaching for the tap and an entirely free way to provide your garden with all the moisture it needs.

If there’s one thing that plants need, it’s water. Unfortunately, the times they need it the most – when conditions are arid, warm and windy – are also often the times when water companies are unable to match supply with demand.

According to the Royal Horticultural Society (RHS), less than three per cent of an average household’s annual water consumption is used on its garden, but during peak demand, as much as 70 per cent of water supplied is being sprayed on our plants and lawns through hoses, sprinklers and drip systems. This can have a serious environmental impact, as it forces water companies to drain groundwater and streams, in addition to driving up water bills.

Fortunately there’s a simple way to reduce both your impact on the environment and your water bills: rainwater harvesting. Yes, there’s quite literally money falling from the skies every time it rains, and best of all, the system needed to collect it comes free with every house. Even in areas with a dry climate, the RHS estimates that 24,000 litres can be harvested from your roof every year – enough to water the average garden many times over.

Collection system

Anywhere that falling rain doesn’t soak into the ground, the runoff can be harvested. So if you have a roof with gutters and a drainpipe – be it on your house, garage or greenhouse – you have a collection system for rainwater harvesting. The roof of an average 25-foot by 40-foot home drains around 2,700 litres of water following an hour of moderate rainfall.

If you have two drainpipes and place a butt under each, each one can divert around 1,350 litres of water for collection. The more barrels you have, the more rainwater you can collect. Just make sure that the gutter stays clear to allow an unobstructed flow, and that the drainpipe has a debris filter at the junction where it connects to the gutter.

Water storage following rainwater harvesting

Most rain falls during the winter months, so following rainwater harvesting, you will need somewhere to store it for use in spring and summer. During the five-month period from May to September, your plants' moisture requirements are likely to be greater than the amount that they get from rainfall alone.

To meet this shortfall, it’s worth investing in a water butt to harvest rainwater from either open or closed drain pipes. If you only have a closed drain pipe, an easily installable rainwater diverter can be used to channel water into the butt.

It is simpler to collect the water if you purchase a butt that has a tap at its base and place it on a stand, whether this is purpose built or home-made using a pile of bricks or blocks. In periods of heavy rain, there can be some overflow, so it is advisable to have bricks or a layer of gravel under the stand to divert water away from the foundations of the structure that the butt stands next to.

Make it easy

Water butts work by gravity – you can either fill a watering can directly from its tap or connect a hose to the tap to water different areas of you garden. However, if you need to water an area that is at a higher elevation than the water butt, or is a good distance from it, you’ll need to use a pump.

To make rainwater harvesting even easier, the new GARDENA smart Pressure Pump is equipped with a 1,300 Watt jet pump which can quickly and reliably distribute up to 5,000 litres of water per hour. A check valve with an optimised suction process ensures that water can be pumped from a depth of up to eight metres in just a few minutes.

It also has two outlets, allowing two watering devices to be connected, and can be used together with GARDENA’s integrated Water Computer MultiControl for time-controlled irrigation.

Make it easy

If you are serious about gardening, the one-off investment in equipment for rainwater harvesting is well worth it. Otherwise, you could be kicking yourself the next time the skies open and all of that free water goes down the drain!