A rotten egg smell emerging from a kitchen or bathroom sink is usually caused by sulphur deposits. As people are unfamiliar are with the odor of sulphur, they identify with the smell that resembles it closest -- rotten eggs. A house cannot function without a steady supply of clean, running water. You need water to bathe, drink, wash clothes and keep important household appliances such as washing machines and dishwashers running smoothly.
A strong sulphur smell emanating from a sink usually indicates a problem with a house's plumbing system. A rotten egg smell emerging from the kitchen sink may indicate that there is a build up of food waste in the kitchen drainpipe. Running hot water through the sink that contains decaying food deposits is likely to make the smell more severe. Unblock trapped food by pouring a chemical drain treatment down the sink. If the smell subsides once the drain cleaner has done its work, then food was probably the cause of the stench. Avoid pushing food down the sink drain to prevent the problem from coming back.
Check the trap pipe beneath your sink if the rotten egg smell persists. The trap is shaped like the letter "S" to prevent unpleasant odors from rising back up the sink outlet once waste products have been disposed of. You can check whether the trap pipe is working by shining a flashlight down the kitchen drain. There should be water present beneath the plughole, indicating the trap is working properly. Contact a plumber to repair the pipe if there is no water present beneath the plughole.
The rotten egg smell may not be coming from your sink. It may be the water running from the faucet that is the source of the smell. This is indicative of issues with your water heating system. These can become ridden with bacteria and impurities over time, resulting in poor quality and bad smelling water emerging from the faucet. Run the hot water tap for a few seconds and then the cold water tap separately. If the stench is more apparent with the hot water, then your heating system is polluted. Contact a plumber to have your system cleansed, and the smell should subside. If the odor is present in both hot and cold water, then there is probably an issue with the quality and cleanliness of your water pipes. Contact a plumber and arrange for the pipes to be cleaned or new lines installed.
Prevention is often more effective than cure when it comes to unpleasant rotten egg odors. Bleach can be an effective means of killing organic material present in your sink's plumbing pipes and preventing offensive odors from rising back into your house. Pour a cupful of bleach down your kitchen and bathroom sinks every three or four weeks. This will flush out any bacteria or mold that may be forming in your plumbing lines.