My water has smelled bad for a few years now and like you've found, it looks like it's due to managanese/iron in the water. I don't know what your filter system setup is but I went with a 3 filter system like this. Previous to installing this system I had a whole house string filter that I used in conjuction with a water softner and another filter system. I could usually tell when it was time to change the string filter as the smell would be very strong. After installing this three filter system, I could tell right away the difference in the feel of the water. I also didn't have any smell either. Like BrokenKnee said, it's possible that the anode rod in your water heater has been compromised. My next step is to replace the anode and totally drain the water heater now that I've cleaned the water as I know that there is stuff in the bottom of the water heater that could possibly cause some issues. If I notice that the smell comes back, I'll more than likely look at adding air to the system.
I'm not really suggesting this specific system as it's on the pricey side, but I would look at the type of filters the system is using. These filters are used specifically for the reduction of Iron, Manganese and Sulfur which gives you your smell.
Home Master Water Filter - HMF3SdgFeC-Water-Filtration-Sediment
1st Stage Filter, dual gradient depth polypropylene sediment filter. 25 micron surface, 1 micron inner core, designed for purity with bacterial and chemical resistance, two separate filter layers for enhanced filter performance, triple the dirt holding capacity of similar sized cartridges, typical life cycle 6, 12 months depending on usage and sediment quantity.
CFdgd2501-20BB-Gradient-Sediment-Replacement-Water
2nd Stage Filter - Radial Flow Iron, Manganese and Sulfur Reduction Filter, Radial Flow design provides excellent iron reduction with minimal pressure drop (<1 psi pressure drop), Easily and effectively reduces Iron, Manganese and Sulfur in water up to 3ppm , Reduces possibility of pipe and water heater damage, Lifecycle based upon iron level.
Cfrffe-20BB-Reducing-Replacement-Water
3rd Stage Filter, Radial flow granular activated coconut shell carbon , Chlorine, chemicals, taste, and odor removal
CFrfgac20-20BB-Radial-Replacement-Water
Thanks,
Greg