Is it in both the hot and cold water?
Try the cold water first. Hot water heaters can produce a sulfur or rotten egg smell in your water. If it is only in the hot water, you may want to seek the advice of a plumber.
Do you notice it at every faucet?
If you notice it when running water at only one faucet, the sink drain may need to be cleaned. Try taking a glass of water and walking into another room. Do you still notice the smell in the glass?
When and where is it occurring?
Do you only smell it first thing in the morning? You may need to flush the line a little each morning before using the water. Water sitting in pipes can sometimes cause an odor.
How do I get more information?
For additional questions or concerns, call 311 or email email@example.com.