Unlike this question, the hot water heater is not a factor as it is happening to joints all over the house. Further all joints are either copper on copper or brass on copper.
I've taken over managing my inlaw's property and it seems every shutoff valve is corroded and leaking. The in laws claim the valves were replaced 5 years ago, and that's just what they look like after five years. I've replaced a few out of necessity, but would like to fix the root problem before changing the rest of the house over.
The area I'm in has pretty hard water due to winter road salting which may be part of the problem. However, I've asked my neighbors, but none of them seem to be having this issue.
What is causing my pipes to corrode so quickly?