the smell comes from the type of water you are using. is it well water from your home or a city connection or a rv park supply. if any of the above have a high content of sulfur in the water, once you heat that water you will create a chemical reaction with the sulfur and you get the smell. only way to not get the smell is to use filters to get rid of the sulfur. most cities use the wind to rid the water of the sulfur. you will see bell towers on top of a water supply tank. what they do is shot the water to the top of the bell and air moving through the sides of the bell dissipate the sulfur from the water. that is one method and the cheapest so it is used a lot. your problem now is to get rid of the smell you have now so you need to buy a water heater clean out tool and follow the instructions on the clean out folder.