Thirst is activated only when 0.8% to 2% dehydrated, meaning drinking only when thirsty results in a state of constant dehydration.

“thirst is a survival mechanism and it doesn't get activated unless you consume like salt or something like that unless you are anywhere from point eight to two percent dehydrated in other words if you are only drinking when you are thirsty then you are constantly dehydrated and you're playing catch-up”