The number of "automatic watering systems" sold over the last few years has increased significantly and it’s good that the RHS point out that it can use up to 75% less water than an average sprinkler.

It uses 75% less as the water dispersed from the water system is directed to individual plants rather than being sprayed over a large area where you are probably watering the path, weeds and other areas not intended to be watered.

The other advantage of a watering system is that you can attach a garden watering timer that will switch on and off as required. If you set this to come on at night then you save even more water. Why? Because water gets longer to soak in to the soil and plants get longer to take in the moisture. If you water in the day the water is evaporating as the plants are trying to take in the water. Therefore more water is required.

Take a look at these pages...
http://www.garden4less.co.uk/automat...ng_systems.asp
http://www.garden4less.co.uk/hozeloc...ion-system.asp

This page isn't navigable from the site yet as it isn't finished..
http://www.garden4less.co.uk/automat...-butt-test.asp

Why you should water the garden at night....
http://www.garden4less.co.uk/waterin...n-at-night.asp

If you have any questions then please let me know.