Those are usually the first words that come to mind when you discover that your sink smells like rotten eggs.
But what do can you do about it?
First of all, you need to define the problem. What you are smelling is very likely to be hydrogen sulfide gas.
The gas is produced by bacteria in the water.
Step one is finding the contamination source.
Take a glass of water from the area you think the smell is coming from and take it outside away from the smell.
Now smell the water.
If it smells, the problem is in the pipes that lead to the water source.
If it doesn't, the problem is likely in the drain.
Continue your detective work with another water sample from a different part of the house.
Does that water smell too?
If it does, the problem is in your water supply. Some wells naturally have water than can smell bad, and the problem can get worse with time. No smell on your second sample? Then you have localized the problem.
But you still have some work to do.
You need to check the hot water, cold water and the drain itself.
Draw both kinds of water and use your nose.
If the smell is coming from your hot water, your hot water heater is likely contaminated with bacteria.
You can try to fix the problem by getting the water in the heater to 160 degrees.
That's hot enough to kill the bacteria, but it's also hot enough to scald your skin.
Also run some of the very hot water through your pipes to kill any bacteria inside them as well.
But be careful.
After about an hour, put the temperature back to 125 degrees or so.
If the smell is in your cold water, bacteria in the pipes is the likely culprit. Time to call a plumber to assess exactly where the problem is and find out your options.
If the smell is in your drain, you can put a couple of teaspoons of baking soda in the drain and chase it with vinegar and then boiling water after a few minutes. The foaming action will eat away at any contamination and the water will wash it away.
Hydrogen Sulfide gas is not the only source of odors for sinks and drains. Other common problems are grease decomposing inside pipes, food particles rotting inside garbage disposals, unused drains where water has evaporated, allowing sewer gas to flow back into the pipes through the trap and unprofessional plumbing work that did not allow for a proper trap.
Some of these are easy fixes and some are not. If you are in doubt, the best thing to do is call a professional plumber before you move forward.