A leaking tap can waste up to 500 litres of water per week and if it's a hot tap, it can be a huge waste of water and energy.
The common causes of a leaking tap include:
The washer: This is the small rubber ring in your tap that stops the flow of water. Over time they can simply wear out or may not have been installed properly in the first place.
The O-ring: This is a part installed in your tap handles to create a waterproof seal. If these get damaged, or come loose, it will cause leaking near the handle of your tap.
The cartridge: Your cartridge is responsible for the flow and temperature of your water and can be damaged by wear-and-tear over time.
The valve seat: This is where the spout meets the tap and can be damaged by mineral build-up and general wear-and-tear.
Many homeowners will replace their own tap washers only to find the tap still drips. It's best to call your local plumber to take a look at the problem. He has the special tools and knowledge to diagnose the problem and fix the tap properly.