Rainwater Recovery - Is it right for me?

Rainwater Recovery

Rainwater harvesting systems can provide water for

  • Flushing Toilets
  • Washing Machines
  • Dish Washers
  • Watering Gardens
  • Car Washing

Sizing a Rainwater Harvesting System

The volume of collectable rainwater (RWHsize) is equal to:

  1. your roof area size multiplied
  2. by the “run off” coefficient multiplied
  3. by the filter efficiency multiplied
  4. by the annual rainfall in your area.

The roof area is calculated by the length times the width.

The “run-off” coefficient is the amount of rainwater that hits the roof that can actually be collected.

A coefficient of “0” means no rainwater can be collected; whilst a coefficient of 1 means 100% can be collected.

Typical coefficients are:

  • Pitched roof = 0.85
  • Flat Roof (smooth surface) = 0.55
  • Flat Roof (non-smooth surface) = 0.45

Filter efficiencies are nearly always supplied by the manufacturers. In the absence of a filter efficiency a figure of 0.8 (80%) should be used.

Monthly and Annual rainfall data can be obtained for free from the Met Office. www.metoffice.org.uk

Example Sizing

The pitched roof area is 20m x 15m = 300 meters squared

The annual rainfall for the area is 600mm.

Therefore amount of rainfall we can collect is:

300 x 0.85 x 0.80 x 600 = 122,400 litres

122,400 / 1000 = 122.4 meters cubed of storage space as a maximum should be installed

Expected Volume

Using our latest technology Rainwater Harvesting systems, which are easy to install and maintain, you can expect to have all your non-potable water provided by rainwater.

However this will wholly depend on:

  • Size of your roof area
  • Annual rainfall
  • The size of your system
  • Your water demand

The average house can harvest 64,000 litres of rain water a year from their roof…that’s 213 water butts!

The average person uses around 18,000 litres of water per annum just to flush toilets and wash clothes,

That means as you re-use your rainwater you save money and you save the environment.

Rainwater harvesting is a logical choice.

Planning Permission

There are currently no regulations that govern Rainwater Harvesting systems; however Building Regulations “Part H” covers the siting of the tank/s and pipe runs, whilst Building Regulations “Part G” covers the internal plumbing.

Water meters are becoming increasingly prevalent and Local Planning Officers are beginning to insist that all new builds and even where properties extensions have Rainwater Harvesting systems

To achieve the Code for Sustainable Homes Level 3 & 4, which is mandatory for all Housing Associations, consumptions levels need to be as low as 105 litres per person per day. The Code for Sustainable Homes Level 5 & 6 will be mandatory for Housing Associations by 2013, and to achieve meet targets, consumption levels must fall below 80 litres per person per day.