The last time I had that kind of smell in the water system of my RV it came from the hot water heater after storage. I neglected to drain it out prior to putting it away from the season. As soon as I pulled the plug the nasty water and smell came rushing out. I just flushed the system with plenty of fresh water and the smell went away. As far as cleaning out the fresh water system, there are very specific instructions on using bleach to clean the system, just do some research on mixing ratios and be sure that you properly flush the system after cleaning.
I had problem with fresh water tank odor. I never travel with a full tank and only load 15 gallons before leaving, but always empty when returning. While fixing another problem in the underbelly, I noticed that the fresh tank was only supported by two straps equidistant from the ends. In between were sags in the tank that left water standing. So I never really had empty tanks. By opening the drain and pushing up the bulges, I got nearly 20 gallons of water out. My remedy was to remove the straps and put 6 pieces of 1/2" angle iron equally spaced. now my tank bottom is flat and I no longer carry old water around contaminating my small fresh water load.
1996 F350 7.3L Turbodiesel
Dually w Banks Powerpack
2012 Komfort 3130
Livin the Life
Chris & Donna
2014 Voltage Epic 3990, 600AH Lifeblue, 1895W Solar, 3K Magnum w/AGS, 3X Micro-Air ES
2018 RAM 3500 Laramie Sport Crew Cab 6.7 Cummins, AISIN 4X4 DRW 4.10 Long Bed Dually 2004 Sportster 1200c