That smell can come normally come from two things. The anode rod in the hot water heater, and an algae that can take hold anywhere in the water supply system.
To determine if it is only in the hot water system, you can try pulling water through the cold water lines (supplying it through the external city water connection) and see if the odor goes away. If it does, then it is localized to the hot water lines and water heater.
If the water system has been dormant for any length of time, it would be advised to "purify" the entire system. This is what I do to treat those conditions, or to purify my water system after an extended period of non-use.
1. Drain the fresh water tank.
2. Pour a cup of household bleach into the tank, and then fill it to capacity.
3. Take a 50' water supply hose, and pour a cup of household bleach into the hose.
4. Connect the hose to the RV and the water supply hose bib.
5. Open the HOT water faucet that is as far away from the hot water heater as possible.
6. Turn on the water supply, and wait until you can smell the bleach at the open faucet. Then close that faucet.
7. Turn on the other HOT water faucets in turn, and wait for the bleach smell at each faucet.
8. Now turn off the city water supply. Turn on the water pump, and repeat pulling COLD water through each of the faucets until you have the bleach odor. Sometimes this is difficult, since you've had the bleach odor from the HOT water.
9. After you've pulled the solution through all the lines, let the system sit for about 8 hours.
10. Drain the system, and fresh water tank. Refill the tank, and repeat the process until the bleach smell dissipates.
11. Be prepared for the wife to complain about what the chlorine is doing to her complexion and hair. LOL
In Yuma, AZ I did encounter contamination in the city water supply one fall when we returned there after their lines had been dormant through the hot summer. Far West Water Company came out and basically did the same thing to their water lines in our RV Subdivision.
Hope this helps.