Got nerd snipped for five minutes, I'm not an expert.
Water Footprint in Cotton 2020-2024: A Global Analysis - International Cotton Advisory Committee
www.publicnow.com/view/CCB3C30C31DE9705ECBD1880A5B7FFE598A8B865?1742503677
Cotton production is often misrepresented, particularly regarding its water consumption, and is frequently labeled a "thirsty crop" based on calculations of water use efficiency-measured as the total water (rainfall plus irrigation) required to produce one kilogram of lint. This study revealed that the annual average water used to produce one kilogram of cotton lint was 8,927 litres, comprising 6,582 litres/kg lint from rainwater and 2,346 litres/kg lint from irrigation water.
Small antidote on a single farm in North Carolina. It seems we still grow cotton without irrigation at all in some places. This is probably really unusual and seems like the kind of thing you'd need to deliberately look for in a farm.
Since the Burlesons don’t irrigate, the wheat cover crop proves particularly beneficial for maintaining crop moisture in hot, dry years. But Andrew says the greatest benefit is that it returns organic matter to the soil.www.farmprogress.com/cotton/burlesons-southeast-high-cotton-award-winner
This doesn't have exact numbers at all, but it's the gold standard peer reviewed* "hemp industry daily" so meh, I'd expect them to be promoting it if anything
“I’ve heard a lot of people promoting hemp as a low-water-use crop, and from what I’ve seen, it’s pretty high compared to other crops,”
hempindustrydaily.com/myth-busting-hemp-needs-more-water-than-many-think/
Cotton as a textile also just isn't a 1:1 replacement for wool (re: the other thread), but I don't think any other plant textiles are either. A shame. But on water use, wool is so much worse than cotton. Probably literally anything from plant fibers is like an order of magnitude better than wool.
*note: not being serious