Every 2-3 rounds. They aren't like normal socks and your feet don't tend to sweat in them.How often do you need to wash them? Genuine question. If I’m paying £30-£45 for a pair of socks, I’d doubt I’d be buying multiple pairs.
I have some, they are great. Instead of moving comfy shoes on because the waterproofing fails I can keep wearing them until they really start falling apart.