I'm on well and septic, have an iron filter and water softener. Recent had smelly water throughout house until I added bleach to the brine tank of the water softener and regenerated. I'm now OK in all taps but two both located in a second story bath sink. Hot water seams OK when first turned on, but cold water is smelly for several seconds after none use.

Have you left the taps run for a while to flush the lines out?

The water is fine after running it each morning and night, but reoccurs. I'm thinking about disinfecting the entire water system starting at the well.