What's the best way to store rainwater?

Crocus with raindrops

With heavy rainfall drenching parts of the UK and hosepipe bans in place, what's the best way to store water to feed your garden?

Gardeners have been given a much-needed lifeline to keep their plants alive over coming months.

Overnight in the South West, Exeter Airport recorded 29mm of rain, more than half its previous April average of 56.4mm. The UK-wide average rainfall in April 2011 was 36.7mm, and 48mm in 2010.

And the wet weather is set to continue, with the possibility of as much as a month's worth of rain falling in Wales and the south of England over the next few days, the Met Office says.

So how can one make the best of it?

The concept of capturing rainwater and storing it for later use is well-documented from pre-Roman times, the UK Rainwater Harvesting Association says.

Where to store rainwater:

Gardner filling watering can from a water butt
  • Standard water butt: Holds between 100 to 300 litres, is a barrel or square shape and has a tap near the base
  • Ornamental tank: Designed to fit in with your garden (shaped like boulders etc). Capacity is between 30 and 300 litres
  • Large above-ground tank: Holds up to 2000 litres, and is a big rectangular shape, that needs to be sited on a flat firm base
  • Large underground tank: Can store several thousand litres of water and requires a pump. Because of size can be connected to washing machine and toilet too

It says the practice died away after mains-supplied water was introduced, but with pressure on water supplies the demand for rainwater recycling systems is rising again.

Sales of water butts have already been surging as hosepipe bans have been enforced, as it is estimated that about 24,000 litres can be saved from the average house roof every year.

Although it takes 12 years to get "pay back" from them economically, they are "the right thing to do environmentally", says Waterwise managing director Jacob Tompkins.

"They are the simplest and cheapest thing to do," he says, "it just fits in to your downpipe. You can gather water in buckets and watering cans as well, if you use it straight away.

"Plants prefer rainwater, as tap water is chalky and rainwater is acidic." He recommends joining more than one butt together to maximise storage.

The Environment Agency's tips for collecting rainwater are:

• Buy a water butt from your water company, gardening or DIY centre

• Fit a water butt on every downpipe on your house, shed, garage or greenhouse

• Increase your storage by connecting several water butts together, or just get one larger butt if space allows

Bishop of Llandhaff Dahlia Plants prefer rainwater as tapwater is chalky

But the water should only be used on the garden, Jacob Tompkins says.

"You should not have problems in the UK with mosquitoes, but if you do, there are special gels and crystals you can add to your butt to stop them breeding.

"Or if you add half a teaspoon of cooking oil, a film spreads across the top of the water also preventing them from breeding.

"People shouldn't drink water from the butt, as rainwater is fine, but what's collected on your roof isn't - it can be contaminated but deposition of particulates on the roof from pollution and cars."

He advises people can also use "grey water", the water from a kitchen sink or bath to feed plants, but says it should be used straight away and not stored.

A lid is needed on any water tank to prevent debris entering it, but also to prevent children falling in. It needs to be secure, and children need to be aware it is heavy, he says.

The Eden Project in Cornwall is one garden that tries to store as much water as it can all year round.

Alistair Griffiths, its horticultural science curator agrees there can be risks gathering rainwater at home.

Rainforest biome at the Eden Project Rainwater from the Eden Project's biomes is used to irrigate the site at night

"If your gutters are not clean, or there's a build-up of stuff in them, that can cause disease in plants if you use the water on them, especially seedlings," he explains.

A rainwater harvesting system is a "more serious" alternative to a water butt, says Terry Nash, from the UK Rainwater Harvesting Association.

"The storage tank would almost invariably be underground, out of sight and be 10, 20, or 30 times the content of a water butt," he says.

How to fit a water butt:

Water butts

There are two ways to fit a water butt:

  • The easiest way is to sever a plastic down pipe with a hacksaw and place the butt directly underneath it - an overflow pipe can be attached to the butt to channel away excess water to a drain or into another butt
  • Alternatively, cut a notch out of the pipe and fit a rain trap and connecting pipe - this will transport water to your butt and allows you to put it in the most convenient place

Nash says if someone had bought a system and installed in three weeks ago, it would be full by now.

"They would have filled a 6,500 litre one... because we've had so much rain over the last four weeks."

However they are more expensive.

Andy Berry, from Acorn Landscapes in Gloucestershire, says some people choose to go "the whole hog" on systems costing tens of thousands of pounds.

"They install a rainwater storage system with filters and pumps, so the water can then be used safely in their house," he says.

Griffiths says the water harvesting and distribution system at the Eden Project has been "designed specifically to capture as much water as possible from its biomes' roofs".

Groundwater is redistributed to the Mediterranean biome and outside biome, while the rainforest biome relies on rainwater, collected in the tank, "percolated" and pumped out via an irrigation system.

But he says for home gardeners, even before harvesting water, there are decisions to be made about how it is used.

"Don't over-irrigate, as it can make plants not resistant to drought... and don't water in the middle of the day, if you water at night there's less opportunity for sunlight to evaporate it,"

He also suggests cutting the bottom off a plastic 1.5 or two litre fizzy bottle and burying it upside down near plants, to get rainwater straight to their roots.

While the wet weather continues, water harvesting will remain a top priority for gardeners, as experts say it isn't enough to bring parts of the UK out of drought just yet.

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