Rainwater harvesting

We aren’t as rich in water in the UK as popular belief (and our reputation for rain) would have it. According to Environment Agency figures we only have 1,334 cubic metres per person per year. This is not a lot compared with France (3,065), Italy (2,785) and Spain (2,775). South east England is the worst off thanks to high population density and low rainfall. The Thames Valley has just 266m3 of water per person per year.

Introduction to rainwater harvesting

We aren’t as rich in water in the UK as popular belief would have it. Compared to other European countries, we are a small nation with a large population and use a lot of water.

The average person in the UK uses 149 litres of water every day, according to Statista, and this puts a strain on supply as well as on fish, wetland birds and other wildlife that rely on ponds, rivers and streams.  Providing clean water to every home in the UK also uses a lot of energy – for pumping and treatment.  Energy is also used to heat any hot water that we use.

To begin with we should look at ways we can save water in our home by using it more efficiently. The Centre for Alternative Energy provides some water conservation adviceTop water saving tips include:

  • Getting a low flush toilet or putting a ‘hippo’ (or one litre drinks bottle filled with water) into your cistern (if you have an older toilet)
  • Turning off the tap when brushing your teeth 
  • Only running your washing machine or dishwasher when there’s a full load, and use the economy setting 
  • Mending dripping taps 
  • Putting the plug in (or use a bowl) when washing hands, veg, or doing the washing up 

Capturing and using rainwater can also reduce the amount of potable  water we use and save us money. Rainwater can be used for:

  • Toilet flushing 
  • Clothes washing  
  • Watering the garden 
  • Washing the car and other outside uses

How does rainwater harvesting work?

Rainwater harvesting can be as simple as attaching a water butt to the down pipe from your gutters and using the water you collect to water the garden or wash the car.  

At the other end of the scale, it can be a pumped system that uses rainwater for toilet flushing and clothes washing, as well as outdoor uses. These systems might be gravity fed or use pumps. 

Water from your roof is channelled via your drainpipe to a storage tank. If you want to use it in your home the water will pass through a filter before being stored and used. More sophisticated installations need a control system to monitor water levels and a pump to get the water to where you want it.  

A system that feeds the home will need mains back up that cuts in automatically when the storage tank runs dry. The plumbing from the system must be kept separate from the mains system and labelled. The storage tank can be at ground level, but it is preferable to bury it, both because it looks better, and to protect it against frost. 

Rainwater should not be used as drinking water. 

Is rainwater harvesting suitable for my home?

More complex rainwater harvesting systems are best fitted when a house is built, or when you are doing significant renovation, as they will need changes to the plumbing system and considerable digging in the garden to bury the tank. 
Whether it’s suitable for you will depend on the size of your roof, the average yearly rainfall in your area, how much water you can store and how much water you use. It will not be suitable if you have asbestos or other toxic materials on your roof. A professional can help you work this out. 

Maintenance tends to be minimal. You should make sure filters and drainage are kept clear and pumps are working.  

Rainwater harvesting systems are permitted development but you should still check with your local planning department that all criteria is met. 

A good quality domestic system should cost between £2,000 and £3,000 according to the UK Rainwater Harvesting Association. The cost of running the pump should also be factored in. 

Once installed the system may save only a few tens of pounds per year. For most homes it is more cost effective to reduce water use than to collect rainwater. This will also reduce your energy use, and your associated carbon emissions. A rainwater harvesting system is also unlikely to be cost effective if you are not on a water meter (as you pay the same for your water regardless of the amount used if you don’t have one).

For homes with gardens that need a lot of watering water butts or a simple grey water diversion system can save considerable quantities of potable water and cost much less than a full rainwater harvesting system.