How to Fix a Sink Leak
Sinks are one of those things in the house that you never think about. That is of course until it doesn't work properly. Luckily since sinks have few moving parts and no electronics or motors there's only a few things that can go wrong with them. Most commonly, leaks are a sink's Achilles heel. But, beause of their basic design, most sinks only leak from four different general areas: the faucet, sink drain, drain plumbing or supply lines. All are, for the most part, easy fixes and all can be done by you.
Identifying the Leak
Chances are you're not trying to fix a leak that isn't already there. You have a drip or a small puddle somewhere. The first thing you need to do is clean up any small puddles and get everything as dry as possible. This will delete any red herrings as you search for the source.
With the water off and your sink basin empty look under your sink. If there is water dripping with everything off chances are its coming from the supply lines. These lines (should) have two female ends, one end threads on to the faucet and the other end threads onto the supply valve. The valve is attached, either through glue, solder or it is threaded on, to the pipe that comes out of the wall or up through the floor. Unless your pipe is leaking any leaks from the supply lines will be at these unions, top or bottom.
If there is no leak here, which rarely is there one, then turn on your faucet and plug the sink. As the water flows check the faucet over. There are only a couple places that a faucet can leak from including the handles, where it swivels and the sprayer (if you have one). Look around any joints in these pieces to see if water comes out. Alternatively, you can lay or wrap a paper towel around these pieces to see if the towel dampens.
If the towel is still dry, look under the sink and see if there is are any drips. Because, the drain is stopped if you notice any leaks it will be from the drain fixture on the sink. These are separate parts in relation to the sink and are sealed using plumbers putty and an accompanying washer and nut threaded on from underneath.
If you still haven't found the leak then chances are you have a leak in the drain pipe. Remove the drain plug from the sink and watch the pipes underneath the sink as the water runs through them. It may help to place paper towels under here as well so you can see where any drips are coming from. All sink drain pipes have several different parts that make up the whole. This may include necks with 'y's for dishwasher hook ups, s-traps, p-traps and so on. Take your time to review all joints as the water drains.
At some point you should identify the leak within the sink and then you can begin to fix it.
Fixing any leaks in the supply lines isn't very difficult but may require you to buy new supply lines. If there is a leak in the supply lines shut off the valves below the supply lines and, using a properly sized wrench or crescent wrench, try to tighten the fittings. If there is a leak here often times this will fix it.
If the leak persists then you may need to remove the supply lines and get new ones. You may need to replace the valve as well. Believe me as soon as you remove the supply lines you'll know one way or another if you need to replace the valves, as you'll have water everywhere.
If you need to replace these valves as well, find the next valve in the line, this will generally be under your house or in an access panel on the opposite side of the wall. Once this valve is off reopen the first valve to bleed off any remaining water pressure. Now you'll need to cut the line and this is where you need to be comfortable with your tools. Using a pipe cutter or handsaw cut through the lines below the valves. This will be done regardless of the piping material you have, CPVC, PEX or Copper.
Once you have the valve cut off you'll need to put a new one on. Traditionally, you would have to glue or solder a new one on, but now there is another option. New fittings, such as those made by Shark Bite® or Push Connect® make life much simpler. These fittings can be pushed onto the clean end of a pipe and, once you feel a slight snap are locked on and sealed. They are much more expensive than a glue on fitting but save an incredible amount of time and are..., well idiot proof.
Once your vavle is put on close it and reopen the other vavle. This will allow you to check for any leaks here. If there are no leak attach the new supply lines. Reopen the valve and check for leaks.
A faucet leak is by far the most challenging to fix and is some cases they are irreparable. Once you have established where the sink is leaking from shut off the water to the faucet and then turn the faucet on to get as much water out as possible.
Many faucets do have the capability to be taken apart. If you look closely at the tops of the handles and the neck you should notice a slight joint. Often in faucets with the 'H' and 'C' on them the plastic grommets with 'H' and 'C' will pop off and a screw will be present. remove the screw and the handle will come off. A similar method can be tried with the neck. However, since there are so many different varieties of faucets out there is this is just a general guideline.
Once you are able to get to the 'guts' of the faucet you should notice a small black rubber ring, known as an O-ring. Often when faucet start to leak it is because these O-rings get worn out over time. The are replaceable and fairly inexpensive. If you are able to get to the O-rings and you can replace them I suggest using a little petroleum jelly and cover the rings. It helps them seal and last.
After replacing the O-ring, replace the other parts of the faucet and turn the water back on. If the leak has stopped congratulations, if not you may need to replace the faucet or see if the manufacturer has a rebuild kit for them.
The sink drain and plug rarely leak but it could happen. This piece is sealed to the bottom of the sink with plumber's putty and a large locking nut from underneath. The first thing to do is to try to tighten the nut using a large pair of adjustable pliers and then check for leaks.
If a leak persists, you may have to remove the drain fixture, reseal it with plumber's putty, and then tighten it back down. First, undue the drain plumbing from the sink drain. Then remove the locking nut from the drain. Finally, remove the drain.
Clear out any and all plumber's putty and then replace it. To get a good seal take a small ball of plumber's putty and roll it between your ands to make a long ribbon that will be able to make a circle about the same diameter as the sink drain and about 1/4" thick. To make the ribbon just do the same movement that you used as a kid to make a snake from play-dough.
Lay the putty around the hole and put the drain back in place. Next, tighten the nut back down. As you do this, any excess putty will squish out from between the drain and the sink, which you can just scrape off with your fingernail and discard or save in the putty jar.
Reattach the drain piping and check for leaks.
Any drain piping leaks are usually pretty simple fixes (if the are PVC pipes). First, at the joint that you have identified as the source of the leak try tightening any nuts. most of these joints are called compression joints. They consist of one side that has a threaded male end, and another piece that slides into that piece and has a nylon ring that is tapered on one end and a loose female threaded piece. As these pipes are fitted together the nylon ring slides up to meet the male threaded end. The nylon ring slides up inside this pipe and as the nut is threaded on, the nylon ring tightens up and seals the pipe.
These pipes can come loose from time to time and just need a little retightening. Sometimes, the nylon ring goes bad and it needs to be replaced. If you have a thin steel drain system parts may have rusted and need to be replaced. If you have galvanized drains this may need to be cut out and replaced back to a solid piece of drain. But, that is a whole other ball of wax. Hope this helps and good luck.