rain water harvesting

Precious Resource | Water facts | How to gain from rain | Saving the World | Drought protection | Reduce your water use

Making the most of the world's most precious resource.

In the UK we are complacent about our water. Our water is cheaper than in many countries and only 22% of domestic properties are metered. It is a tradition for our European neighbours to mock us for our wet summers. Yet in fact the UK is classified as a country with insufficient water. Madrid and Istanbul have more water available per person than London. Global warming is accepted now whether man-made or cyclical, and so we must make the best use of our precious water and prevent the situation deteriorating.

Rainwater harvesting has a significant role to play in doing this. The Code for Sustainable Homes came into force for state-funded housing in April 2007 and could be applicable to private housing in 2008. This Code assesses homes for sustainability in 9 categories, including 2 to do with water. One aims to reduce drinking quality water consumption and the other to reduce flood risk. Currently 30 to 50% of the 160 litres of water each person uses a day need not be drinking quality water. Using rainwater from our own roofs would greatly reduce consumption. Collecting rainwater also contributes towards avoiding floods. Other new Building Regulations may impose rainwater harvesting in large building projects in the south and east. But whether as a householder or a concerned professional, we can move ahead on our own account without waiting for official rules and regs. And whether with a 200 litre water butt to water seedlings or a 10000 litre storage tank linked to the home, we can all maximise our use of rainwater and relieve the water shortage in this country.

Water Facts

Imagine yourself in swimming in a pool 7 metres long, 4 wide and 2 deep: not a big pool but large enough to take some good exercise. It contains the amount of water it is estimated you use every year in the UK: 58 400 litres or 160 litres a day. How do we manage to use so much?

Water Use in the home

Average Bath 100 litres
Average WC use daily 50 litres (old WCs use 9 litres per flush, new dual flush 4 or 2.5 litres)
5 min shower 33 litres (more like 100 with a power shower)
Leaving tap running eg washing up or cleaning teeth. 5 to 10 litres a minute
Dishwasher load 25-60 litres
Clothes washing load 70-120 litres

Water Use outside the home
And so that’s about 160 litres down the drain before even going in the garden. Normally outdoor use of water is only 6% of water consumption. But at peak times in a dry summer this rises to 70%. The hosepipe is the villain. Depending on use, it flows at around 1000 to 1400 litres an hour. Connected to a sprinker, it is a wasteful and ineffective way of watering. Using a trickle or drip system is a much better way: water is absorbed slowly and penetrates more easily to roots, there is no evaporation, and it can be directed to specific plants. And on average a 100 metre length only uses 55 litres an hour.

How to gain from rain (or what's in it for me?)

OK, so at long last more and more of us are realising that our water is precious. The UK has been spoilt so far: we have had cheap and plentiful water, but this is changing. We need to use water more efficiently. But however “green” we are, we all want to know how much it will cost us and save us. The summer of 2006 showed a lot of us what it was like having a prolonged hosepipe ban on watering gardens and washing cars. Current proposals will extend the ban to activities such as filling swimming pools, ornamental ponds, hot tubs, cleaning drives, patios and windows. With long term forecasts predicting an equally dry summer for 2007, collecting rainwater effectively is becoming an important consideration. Installing a couple of 200 litre water butts may help to keep precious seedlings alive during a hose pipe ban. For those with large and expensively-planted gardens, regular watering becomes crucial during a drought. And owners of pools and hot tubs may find them unusable just when they want to use them most. The larger the tank installed, the more security in a long dry summer.

Further up the scale, a full rainwater harvesting system including, for example, a 3000 litre tank plus accessories for use in the home (filters, pump, control panel) might well cost £3000. And if the tank is put underground and plumbing alterations made to connect the system to WCs and washing machines, then the cost could double. This seems a hefty investment when we’re used to getting our water for so cheaply. But as we keep saying, the situation is changing: a rainwater harvesting system may seem a large investment with no immediate financial gain, but as an investment in your home’s future and improving the environment it is without doubt worthwhile:

  • The recently introduced Code for Sustainable Homes will (along with other categories) assess homes for reduction in drinking water consumption and flood risk. Homes with effective rainwater harvesting facilities are likely to be viewed more favourably by potential purchasers. The investment will be worth it in the resale price. From June 2007, all property being sold will need a “Home Information Pack”. This includes an “Energy Performance Certificate” giving current heating, hotwater and lighting costs and later may include a water use assessment. Again rainwater use will be viewed positively.
  • water bills estimated to rise 10% in the next 5 years
  • currently only 28% of domestic households are metered but all new homes are now required to have them; records show that metered homes use 10% less water; having a meter and using rainwater could reduce your water bill;
  • With the recent huge growth in "being green", homes with rain water harvesting facilities are likely to be viewed more favourably by potential purchasers: the investment will be worth it in the resale price
  • Likelihood of Government grants and/or tax rebates for homes installing rainwater harvesting systems. The pressure is on to persuade the Government to implement grants such as exist in Germany where in some areas a grant of £1000 is given towards the cost of installation. Germany now has 50 000 rainwater harvesting systems installed every year (500 000 in total).
  • Even if the growth in rainwater harvesting would eventually reduce revenues for water companies, this is offset by the saving to them of constructing new reservoirs or desalination plants to cater for the ever-increasing water demand. Thames Water hopes to build the UK's first desalination plant supplying 150 million litres a day. A little bit of investment by householders in the south and they could be saved the trouble.
  • And you can keep your garden green and make your life greener!!

A 2003/04 survey of English Housing found that 18, 908. 000 households have a garden, patio, yard, roof terrace or large balcony: just think how much water we could save if everyone used rainwater!

Save the World

Are you frustrated that governments, international agencies and leaders seem unable to do anything about global warming, the depletion of our natural resources or preventing natural disasters? Would you like to do something about it yourself? Maybe it's the time to stand up and be counted. Express your individual responsibility for the destiny of the world. You are probably already co-operating with your local council in recycling as much waste as possible. You have double glazed the windows, increased insulation and turn lights off whenever possible to reduce your energy consumption. Are you thinking about solar or wind energy? Yes, but there seem to be some obstacles, not least of which is how little the sun shines in the UK at the times you need the energy.

Now things are a little bit clearer for rain water harvesting. We have high levels of rainfall. Collecting it is simple from an engineering and planning point of view. So you have a simple means of reducing your dependency on the mains water supply, and increasing your protection against the effect of droughts on your garden watering, car-washing and other domestic use. You don't need to use drinking water to flush your toilets or supply your clothes washing machine! In fact in an average home 45% of domestic water use does not need mains water at all... rain water is fine.

Put it another way. Does it seem ridiculous to you that a money-making conglomerate processes water centrally, pipes it huge distances to get to your house, and loses a high percentage from pipe leaks on the way? What a waste of energy. Then you dump 99% of it down the drain when you've used it, to be piped back to that same company in a sewer. Most homes in the UK will soon have a water meter, so they'll be charging you for what you use. Why not process the rainwater from your own roof, use it around the house, and reduce your dependency on the water company.

Whatever your feelings on the environmental and economic issues, you can take simple steps today to use your own rain water. The simple act of installing a water butt in the garden, will not only give you water for the garden when it's dry but will also reduce your use of mains water for watering the garden. Or take a bigger step and ask us to calculate the cost of a built-in system, header tank in the roof, and piping to be able to reduce mains water consumption in the house.

Protect yourself from droughts

Rainfall in the UK varies between 550 and 3000mm a year. However, the high rainfall tends to be in the north and west where few people live. Most people live where rainfall is between 600 and 800 mm a year. London is actually drier than Istanbul and Madrid. In fact it is predicted that it will become wetter in the north and west, and drier in the south and east. The Environment Agency has concluded that the south and east are already past sustainable levels. It will be wetter in winter and drier in summer. In the summer of 2006, , this was not the case, with the dry summer preceded by a dry winter compounding the water shortage resulting in the well-publicised water restrictions. And in 2007 the government is proposing to extend the hosepipe ban from just watering gardens and washing cars to include filling swimming pools, ornamental ponds and hot tubs, and cleaning patios, drives and windows. Furthermore, long term forecasts are predicting an equally dry summer for 2007.

But with a water tank and an effective irrigation system you could keep your garden going throughout a drought. For example, with a 5000 litre tank and a 100 m long drip system, you could water for an hour a day for 90 days before the tank ran dry, with 1500 litre tank, for @ 30 days, and with a 650 litre tank for @ 10 days.

Reduce your water use

Even if you install a rainwater harvesting system, this should not stop you trying to reduce your water use: In the garden:
  • Use a drip or trickle system directed to specific plants rather than a sprinkler : a sprinkler uses 1000 litres an hour whereas a 100m length drip system uses on average 55 litres an hour
  • Use a timer
  • Never water in the heat of the day: evaporation will reduce the moisture rapidly, and the plant may even be worse off
  • Put as much compost or mulch as possible round the base of plants to conserve moisture
  • When planting shrubs and fruit trees, put a 30 to 40 cms length of hosepipe into the ground next to stem so that when watered down hose, moisture reaches roots
  • For smaller plants and vegetables, dig in a small flower pot next to them which allows water in it to percolate slowly down to roots
  • Round any plant, shrub or young tree, build up a shallow circular ditch round stem, so that water will stay rather than flow away at once. This is particularly necessary on slopes
  • Gently break any hard soil surface round a plant (taking great care not to disturb roots), so that water can get in
  • Cut lawns less frequently and with a higher blade in dry conditions. And remember that however brown it looks, it will recover. Resist the temptation to use a sprinkler!

In the house

  • Have a shower instead of a bath, and use 33 litres (for a 5 min shower) rather than 100 litres. Watch out for power showers though: nearly 100 litres for 5 mins!)
  • WCs. Old WCs use @ 9 litres per flush. Put plastic bottle in cistern to reduce flush volume. New dual flush WCs use 4 or 2.5 litres per flush
  • Don't leave taps running: 5 to 10 litres a minute can vanish in a minute while you wash your teeth or rinse fruit.
  • Replace worn washers: a dripping tap can waste 4 litres a day.
  • Think before you turn on the hot tap: a litre or 2 can flow away while you're waiting for the hotwater to come through.
  • And a hint that's a pleasure to follow! Fully load a dishwasher rather than wash by hand.

Precious Resource | Water facts | How to gain from rain | Saving the World | Drought protection | Reduce your water use