Some leaks are easy to notice, and a leak under kitchen sink is one of them. The puddle of water that appeared on the bathroom floor isn’t easy to ignore.
However, just because the damage is in a noticeable place doesn’t mean you should let it be.
Any leak and plumbing issue can cause severe damage to the structure of your home. The worst part of it all is that not all the damage is covered by insurance.
This is why you should always know how to locate and fix a leak under kitchen sink. Some problems might even be resolved without calling a professional!
How to Locate a Leak under Kitchen Sink?
Before you learn how to fix a leak under the kitchen sink, you must know how to locate it. Here are the most common kinds of leaks:
- Drain leak
- Water supply leak
- Faucet leak
- Leaky P-Trap
- Damaged washers
- Broken reverse osmosis system
- Clogged or damaged pipes
Below, we have explained how to locate most of these leaks. We will also give you a few bits of advice on how to repair them – and if you can even do that by yourself.
A drain leak is the most common one, and it’s fairly easy to locate. Turn the water on, then drain it out of your sink. If you notice any leaks while the water is draining, then this is causing the problem.
Chances are you have a drain blockage, or that something inside it is corroded or rusted.
Most sinks have a drain sealed with the help of a plumber’s putty. This putty prevents leaks, and it’s good to have it on.
However, as time passes, the putty can dry out. Sometimes, it was too thin, to begin with, and it simply couldn’t hold on that amount of water.
If any of these is the issue, we suggest calling a professional to help you out. Replacing a putty isn’t recommended, and you should instead remove the drain altogether.
Sometimes, the problem lies in loose nuts that are located on pipes’ meeting points. Make sure these nuts are tightened all the way before you assume anything else.
Loose nuts can cause serious leakage, but they are easy to fix. Don’t waste any money if you don’t have to.
Water Supply Leak
Water supply leaks are also a typical kind of damage to the kitchen sink. To locate it, do the same things as with drain leaks – let the water run and try to drain it.
If the water isn’t draining, but you notice a puddle appearing under the sink, then you have this problem. A faulty pipe or joint usually causes water supply leaks.
Another way to know you have a problem with a water supply is if the leaks are constant.
A kitchen sink typically has two water supply connections – one for cold water and one for warm water.
Sometimes, there is a third connection, as well, if your sink has a separately connected sprayer.
Any of these connections can break, corrode or rust, and cause water to drip.
These leaks usually go under the radar until they soak everything in the storage under the sink. This is because the connections are rarely in a visible place.
A failed connector gasket is also a common cause of a water supply leak under kitchen sink. If this is the case, replace the gasket.
This should prevent any further leaks. Sometimes you don’t even have to replace it – just make sure everything is tightened up.
If the leaks keep on occurring, contact your local plumber. When the problem is in the corroded pipes, there isn’t much you can do otherwise.
You can usually spot this leak with no problems what so ever. If the puddle appears when you turn on the water, you can be sure this is the problem.
Sometimes, the leak can occur underneath the sink. You won’t be able to spot it without looking under the kitchen counter.
If the water runs from the faucet handle, you likely have some damage to the O-ring. The O-ring is a small disc affixed to the stem screw that keeps the faucet handle in one place.
This is one of the more common faucet leaks, especially if you have a cartridge faucet. The O-ring isn’t the most resilient part of the faucet.
It can easily become loose or worn out after a few years of using the sink. Luckily for you, replacing the O-ring isn’t difficult, and you can usually do it yourself.
The problem might also lie within the valve seat. This is usually the case if you notice leaks near the base of the faucet.
The valve seat connects the tap and the sprout, and it helps the compression mechanism. When the water accumulates in it, it can corrode and rust.
Over time, this causes enough damage for the faucet to start leaking. Sometimes, you can replace the valve seat by yourself, but it would be best to contact a professional.
Also, we’d advise you to call a plumber to clean the valve seat regularly. This can prolong the life of your kitchen sink.
Look under the kitchen counter where the sink is. Do you see the curved pipe section there? That is known as the P-trap.
It prevents bad smells from exiting the drain. If you notice bad smells together with the leak, this can be a telling sign that your P-trap is clogged.
Identifying this leak can be difficult, though, especially if it’s not followed with foul scent. This is because the P-trap is hidden from the eyes, so it’s not the first location we would think of.
The P-trap can get clogged over time, causing water to leak. The culprit behind this is usually disposed food, debris, and gunk.
All of these block the water drainage. Try unclogging it with chemicals or with a plunger. This may be enough to stop the leak.
Also, P-trap can rust over time, especially if it’s made of metal components. If this is what happened, you should replace it entirely.
Once again, this is a job for a professional plumber.
Another common reason behind a leak under the kitchen sink are worn-out or damaged washers. This is especially common with compression faucets. And yes, using a touchless faucet is a good choice.
Washers are rubber rings that press the valve seal every time you turn the tap on. They are under constant friction, and this can make them worn-out.
When this happens, you can easily see the leaks around the spout of the sink. You don’t have to call a professional to fix this problem. Simply replace the washers.
Make sure you have the replacement washers in the same size! If the new ones are too thin, the sink may leak again.
Broken Reverse Osmosis System
Reverse osmosis water filtration systems are an inexpensive way for you to have clean and fresh drinking water.
At the same time, they need a very low amount of maintenance, and you don’t need to give them constant attention. This is why many people have them installed in their kitchen.
However, even these systems can break, causing puddles on the kitchen floor and inside the cabinet.
To locate them, look for drips in hoses connecting the system to the sink. Another typical place to look for is a leak in the refrigerator’s water dispenser or your ice maker.
Clogged or Damaged Pipes
The most serious culprit behind a leak under the kitchen sink is your sewage system. Sewage pipes can last for a very long time.
Most of us will move out of the house before the lines get old enough to break. However, this can happen.
While it’s rare for clogged pipes to leak only under the kitchen sink, it’s possible. This is done when the water can’t go through the system, causing leaks.
Usually, this leak can be noticed on the wall behind the sink. If any water stains are appearing, pipes are the likely reason behind it.
Sadly, this problem can be expensive, and you should contact a professional for help. Don’t mess with pipes alone, as you can only increase the damage.
So what to do with the leak under kitchen sink?
While smaller leaks and dripping don’t look like a huge issue, you should never hesitate to fix it. Water can cause great damage both to your house and your health.
It can damage the home structure, ruin the walls or the flooring, or cause the parquet to rise.
Not just that, but water causes mold, which can be extremely damaging to your health. 
Leaks underneath the kitchen sink can be the sign that there is something severely wrong with the sewage system. If you leave them be, you are risking serious problems that will be ten times more expensive. 
When you aren’t sure what’s causing the leaks, don’t fear to contact a professional. Only this way you can be certain that you did your best to prevent further problems.