This is not the case. It is very rare that I have ever felt thirsty. It has been an issue my entire life, often with seriously negative outcomes. Every day I have to make a conscious effort to ensure I drink enough water. I can never rely on how I feel; I always have to depend on what intake I have measured.
Not OP but as someone who would regularly consume way too much water to the point it was causing me adverse effects, this is my experience:
When I was properly hydrated I'd still be mildly thirsty.
When I have been overhydrated I'd keep getting thirstier.
And when I was getting close to being on the dehydrated side I'd get mildly thirsty.
But when I would actually start getting dehydrated, the thirst stopped.
It sounds backwards and weird but it's a thing and it's really quite problematic (and it's not that uncommon). I think it technically falls under the name polydipsia but it's more a symptom of any number of different biological quirks or disorders than anything specific in of itself.
When it comes to how one notices they are dehydrated when they aren't feeling thirsty, you tend to get good at picking up on the signs (skin turgor test, headaches, dry mouth, etc) and you also tend to be pretty cognizant of how much water you consume in a day which makes it pretty easy to self correct early.
> People's response to dehydration or over-hydration is not uniform.
Of course not, and I have hopefully stated clearly enough and frequently enough that I'm talking about a general rule to which there are many exceptions both ways.