It's not a small amount of water by any means and it's just one of the various polluting factors in its production. The average young american buys an average 10 shirts per year and this number keeps increasing.
One of the biggest disasters ever, the draining of the sea of Aral (back then shared across 7 countries) has been caused by the insane water needs of cotton farming in Uzbekistan.
So yes, not only the water there has been lost forever, and millions have been impacted in their health, livelihood, farming, etc, and all for what? Shoving $5 t-shirts for the fast fashion industry?
The cotton industry is actually very harmful for the planet, not just in central asia, but those are the many insanely huge problems that people don't want to talk about, because got forbid we stop shoving our closets with low quality junk fast fashion that we quickly forget exists.
And all of this goes back to my point. Consuming stuff is toxic for the planet, the easiest way to curb the evil impact we have on it is to at least try to understand how we could easily curb it with limiting our everyday actions.
Not only you can substitute beef for pork, pork for poultry many times and have a positive effect, you can also decide to buy better clothes that fit you better and last longer. And many other things.