This is a really good guide too:
Interactive house : Save water : Severn Trent Water
Some quick facts:
Sink
Did you know...that a tap left dripping for a whole year can waste 27,000 litres of water? This is usually because of a faulty washer and can be easily fixed.
Toothbrush
Simply turning the tap off whilst brushing your teeth and washing your hands can save over 5 litres of water every minute. If everyone did this we could save enough to supply 450,000 homes with water each year.
Toilet
Did you know...The toilet is one of the largest water users in the home, using up to 43 litres per person per day (33% of your daily use).
save-a-flush
Get a free save-a-flush from SaveWaterSaveMoney - If your toilet was installed before 2001 and has a 7.5 litre flush or more, you could save 1 litre every time you flush by fitting a FREE ‘save-a-flush’ bag.
Shower
Showering for one minute less than normal could save up to 10,000 litres of water in a year