A rotten egg smell from your sink usually comes from bacteria growing in the drain or a dried-out P-trap. Run water for 30 seconds to refill the P-trap seal which blocks sewer gases. Clean the drain with baking soda and vinegar followed by boiling water. A failing anode rod in your water heater can produce hydrogen sulfide gas in hot water lines. Check if the smell occurs only with hot water which points to the water heater.