Fixing a faucet leak
This simple guide is intended as a rudimentary way to find the right repair kit for a DIY project IF you already know a little about the basics of plumbing.
First let me suggest that if you don’t know what you’re doing, call a licensed plumber, as you can make things a lot worse by meddling around with the faucet if you’re not familiar with its inner workings. Calling a plumber can save you a lot of money in the short and long run, especially if the problem is hidden behind a wall or out of sight, such as seeing water damage under your sink, but not finding a leak.
Ok, if you are somewhat "able" (or handy), more than likely you'll know you have a worn out washer, or cartridge, or perhaps it’s the O-rings, etc. Normally you can find a repair kit, depending on the manufacturer, which will contain all the usual objects that tend to wear out.
There are two kinds of faucets, two handed and single handle, if you have the former decide which side is leaking by feeling if it’s hot or cold. If you find that it’s the cold side, then shut off the cold water flow under the faucet. If it still leaks then shut off both sides, and drain the valves.
If you have a single lever faucet, shut off the water, take the handle off, and just take out the cartridge, and bring this with you to the hardware store unless you see a manufacturer's label or know which one you'll need to replace it with.
Whether it's a single lever or two handed faucet, look for some type of sticker or label on the unit underneath to discover the manufacturer to know what kind of kit you need. If you cannot find one, just take a picture of it, and that will usually suffice for any major hardware store’s plumbing specialist to tell what kind you’ll need.
Go and get the kit and proceed to follow the instructions, basically reversing the steps you took to take it apart.