The sulfur smell of rotten eggs is caused by possible bacteria or debris laying in your pipes and or drains. If you notice that the odor is coming from the drain and not the actual water, it could be because bacteria is laying in the elbows/curves with in your drain pipe. Try pouring some chlorine bleach in the drain to remove the bacteria. If you notice that an odor is coming from the water pipes themselves, it might be coming from your hot water heater. This can happen in the cold as well as the hot water. It could be that your hot water heater needs flushed out. When your hot water is used, cold water flows into the hot water heater to replenish it. When the water heater is full, it shuts off and any water left in the line can back wash out into the water lines. As your hot water heater was filling it stirred up any debris that was laying in the bottom of your water heater. This debris can also backwash into the lines. Again, if you haven’t drained your hot water heater in some time, 6 months or more, you may want to try this. Another thing to check is the aerator on your spigot. Remove the aerator/filter at the end of the faucet, clean well, and reattach. Water heaters are another source of H2S(Rotten Egg Smell) when the magnesium rod in the water heater reacts with sulfate in the water and converts it to hydrogen sulfide gas or when the temperature is lowered in the water heater to save energy, allowing sulfate-reducing bacteria to live in the heater.