What could be the root cause of metallic odor in water?
Why don't you send a sample of the water in for a lab analysis? You can have the sample tested for common metals: copper, zinc, iron, magnesium, etc. If the results come back high in a certain type of metal that may help you determine the root cause. Sometimes pipes can leach into the water, or cause build up of minerals. I would look into this as well.
I would have your tech for the water system come check out the system to make sure all the filters are still good. It could be the filters need to be changed. I would also suggest sending a water sample to the lab to test for heavy metals.
You either have a water filtration system not functioning or it is the piping after water treatment. All the treatment you suggested should remove just about everything in the water.
As others have mentioned send a sample out for analysis and see what they come up with. But, look at your filtration system and your piping after the system.
Do you add minerals back in at the end of the filtration process? Excess potassium can cause a metallic/fishy taste.
Extensive water sampling and sensory is required from different points.
1) Bowell water
2) From storage tank
3) Before and after filter
Put some triangle sample in sensory.
If metallic smell start just after filter then need to look into only filter parts, material, cleanliness.
Regards
What is your source of water ? This may be due to high Iron/Fe content of the source water. Do a complete chemical analysis for your source water. If the Fe (Ferrous) content is high, use Green Sand filter (Manganese ore) in your water treatment system.