Brand new - never been used stainless steel briage pot pitted with one 6 minute water boil on my gas range
This is not pitting, this is scale. You can't prevent it, no matter what kind of pot you buy.
Washing/scrubbing won't really help. Get a descaling agent - no need to go for the expensive ones, maybe just get some citric acid in bulk - and descale whenever it builds up enough to bother you.