If your tap water smells like sulfur or rotten eggs, there's probably sulfur bacteria and hydrogen sulfide gas in your building's water supply. If you only smell it when you turn on the hot water, it is highly probable it's a problem inside your hot water heater. In most instances, the water is still safe to drink, but hydrogen sulfide can damage your pipes as it is corrosive to many types of metal. It can cause black stains on silverware and plumbing fixtures.
Drain your water heater, and then turn on the hot water taps and let them all run for about 10 minutes to clear out the water still in the pipes. Raise the temperature of the hot water heater for 145 degrees for eight hours, but only if your hot water heater has a functioning temperature and pressure relief valve. Be sure to warn everyone in the household that the water will be unusually hot, and after eight hours, turn your water heater back to 120 degrees and not less. Less encourages bacteria growth, but higher than 120 can result in scalding burns.
If this doesn't solve the problem , then you may have to get a plumber to replace the magnesium anode rod -- if you have one -- with an aluminum one in your hot water heater.
If the smell is limited to the kitchen sink, then you have a partially clogged drain or a dirty garbage disposal.