The older taps that were fitted with rubber washers open and closed by the constant screwing of the head up and down inside the tap body. This always caused the rubber washers to wear and fail, which meant that you always found yourself turning the tap tighter and tighter to stop the water from flowing. There are new more modern form of tap inserts that replace the old rubber washer, they are called ceramic discs, and with these fitted all that is needed is a 1/4 turn of the tap or shower and the water is shut off straight away. This means no more difficulty sopping the water flow. Like lots of things they can fail. If you are not confident to replace the cartridge, then call a professional like Archway Plumbers who can fit the cartridge. The two ceramic discs each have a hole so as a tap is operated one moves with the handle and the other one is still. As the holes line up, the water flows. If a leak occurs the ceramic discs have suffered some damage and the holes not in line. This means a cartridge replacement is required. They are ‘handed’ for hot and cold so there is a specific one for each. A professional tradesman like an Archway Plumber can replace taps and other fittings. To start, isolate the water supply to the taps. Drain the water away through open taps. Take the heads off the taps. There are two different types, the first is a push on fitting and the second is fitted with a screw. Hold the tap body so that when you undo it, it will not turn with the turning action. Take out the cartridge. Don’t forget the orientation either left or right mentioned earlier. Visually inspect as it could be just debris inside and may just need cleaning. If not, replace the cartridge. Visually inspect the seal for damage. Reassemble and return the water supply to check for correct operation and leaking.