Taps drip. It's inevitable, like death and taxes. They

seal using a rubber ring screwed down over the end of a

metal pipe. Sooner or later the rubber is going to go hard,

split or just wear away and it will no longer seal. Then

water seeps through, and the tap starts dripping. Left

alone the problem gets worse as the water wears away the

valve seat. Then you'll have to either re-grind the valve

seat(Do you own a valve seat re-grinder? Who would?) or

replace the tap. Tedious in either case. But, it need not

happen. Many taps now use ceramic discs.

How They Work

Instead of blocking the pipe by squeezing a piece of

rubber onto the end of it, there are two slotted ceramic

discs held down over the water supply pipe. The bottom disc

doesn't move, while the upper disc is rotated over it by the

tap mechanism. When the slots align the the tap is on, and

when the slots don't align, the tap is off.

Why Are They Better?

There are advantages to this approach. The main one is that

the discs are very hard and withstand the erosion of water

very well. Hence they last much longer before needing

replacement. Also, because the water flow is between the

two discs, it's the discs that wear not the tap body itself.

Because of the arrangement of the discs, it only requires a

quarter turn to go from fully off to fully on and the

operation of the tap is very light. This has the advantage

that they are easy to turn on with the back of the wrist

if you have dirty hands or for people with restricted

movement.

Where they are Used

The ease of operation and the long life mean that most good

quality sink mixer taps have been made using ceramic discs

for a while, but basin taps with ceramic discs are

surprisingly less common. The more use a tap gets, the more

attractive the use of ceramic disc technology becomes. This

is doubly true in hard water areas, which can be murder on

traditional taps.

Disadvantages

There are a few disadvantages. The discs do eventually wear

out, but manufacturers seem to have standardised, so it is

reasonably easy to get replacements. Basin taps are

sometimes handed and sometimes not, and it can be annoying

to have to work out which way to turn the tap in order to

get water. They are also more expensive and not suitable

for very low water pressure. The only other disadvantage

is that if you are used to the old style taps, which need

a number of turns to turn fully on, you may inadvertently

turn the tap on more than you intended, you can get a

unexpected full-on jet of water. Embarrassing!