Install a rain water butt in the garden for watering your plants.

You can buy a kit which is very easy to install. It takes rain water from your roof gutter down pipe and fills the water butt. When the butt is full a clever valve diverts water back down the drain. If necessary you can link several butts together with a butt connecting kit.
The kits will come with full fitting instructions, however a few point are worth highlighting:
NB The rain water pipe is the one that comes down from the roof.

- On most kits you will have to cut out with a saw a small section from your down pipe for the diverter valve to locate in. You may need to fit extra pipe brackets when you have done this to keep the down pipe firmly secure on the wall. These are available at most DIY shops

- The height of where you position the diverter is important so that the butt fills to the top then diverts. Study the fitting instructions before cutting your pipe!!! It should be just below the level of the top of the barrel when in position on it's stand. Too high and the barrel will overflow with water. Too low and the barrel will only part fill.

- On the water butt make sure the connection to the tap at the bottom and the connection to the diverter pipe are water tight. They should come with rubber seals. If they aren't fully water tight use a little silicone seal before you tighten them up.

To buy Butts and down pipe connector kits on line try http://www.waterbuttsdirect.co.uk/