Using a spanner, take off the tap’s cover to remove the handle. You’ll probably find this under the hot or cold sign.
Undo the screw and remove the handle. If the tap has a metal cover, unscrew it by hand, or use a wrench or tap spanner.
Unscrew the tap bonnet, and completely remove the headgear. You should see a large body washer, o-ring and jumper valve. The jumper valve should fall out.
Replace the body washer, the o-ring and the jumper valve with new parts. Apply a tap lubricant to the spindle and valve for better sealing and smoother tap operation.
Refit the bonnet and spindle. Be careful not to over-tighten the nuts.
Put the tap back together, turn it off, and turn the water main back on. Now check the tap to make sure it’s no longer leaking. Now you can step back and admire a proper job, knowing you’re not wasting a drop.