If you are noticing the smell of rotten eggs, it is possible that your water or sink drain is contaminated. It could also be that the drain is clogged or partially drained. When sinks are clogged, they drain slowly, which can cause bacteria to build up in the p-trap and create the hydrogen sulfide gas.
A smelly sink is usually caused by bacteria build up from grease, fat and food which have been flushed down the drain. These will then get stuck in the pipes causing the familiar rotten egg smell.