Okay, the sink in your master bathroom is leaking. Not bad, but the drip, drip, drip is driving you more crazy than when your kid(s) keep singing that one song, over, and over, and over again. There are a couple tricks you can do. Put a towel in the sink. That will keep the drip at bay for at least as long as it takes to go to sleep. But in the morning you will have a sopping wet towel to deal with.
The other step is to fix it. You can call a plumber, but this is expensive. This can be fixed for less than $20 and takes you less than 10 minutes.
The first step is to turn off the water. The valves are under your sink against the wall. I recommend turning off one and see if the leak has stopped. If not, turn that on and the other valve off. In theory, the leak will have stopped when one of the valves was off. If not, turn both valves off. Then pop the cover off the sink handle, which controls another valve that sends the water out of the faucet.
Note: my sink has separate hot and cold water valves – if you have a single valve, these instructions should still work, but you will have to modify them as needed.
Once that cover is off, there should be a screw under the cap.
Undo the screw and take off the handle.
There may be plastic dilly bobber under the handle, which allows the handle to turn the valve. Take this off and set it aside, you may need it later.
There should be a nut too, use an adjustable wrench to take off the nut.
Once the nut is off, use a small flat edge screwdriver to pry the valve out of the seat. If you are lucky, everything will come out in one fell swoop. If not, you may have to pull some things out. Try keep everything in order so you can put it back together if need be.
This is the valve taken apart. The first thing you can do to fix this is to clean the o-rings (the o-rings are the black rubber rings around the valve). If the o-rings are dirty, they can cause leaks. Clean them and put everything back together and see if the leak has stopped. If not, you need to replace it. So, take it back out.
Now, you need to go to your hardware store for a new valve. Look at the brand of sink you have, it will narrow your search. Also, take your valve, and/or take a picture so you can get the valve you need. Sometimes the valves are hot and cold, so be sure to get the right one (or get both).
Putting the new valve back in the sink is easy, just put it in the sink. Put the nut back on, put the white dilly bobber back on (if your new valve didn’t come with one), put the handle back on, screw the screw back in, and then pop the cap back on. I replaced both valves on my sink. It took me less than 3 minutes to do one, including turning the water back on and back off.