Others have already posted some of the direct effects. There’s also an indirect correlation effect. Some vegans are “environmental vegans”, who are more likely to abstain from alcohol or reduce alcohol use for environmental reasons. I’m not vegan myself, by I get the impression it takes a lot of effort to make the leap from vegetarian to vegan, and those with the gumption/perseverance to make that sort of commitment are likely aware of the environmental impacts of the alcohol industry. The metastudy combined studies that use real consumption data, not just lists of what things a person in a category is “allowed” to consume, so it likely incorporated low average alcohol consumption by vegans.
I’ve been vegan since 1997, and this is not a core vegan issue (if the drink is vegan and therefore animal-free). It’s a whataboutism tactic to divert and blame, like with almonds and avocados. Or it’s like saying vegans don’t drive cars.
I guess for distilled liquors, that is an issue to an extent. Generally, in “normal” brews (Yes, I am displaying my prejudices here!) the water demand is pretty much equivalent to growing the fruit/grain that is fermented, plus, for beers, the water that extracts to fermentables, but that is what becomes the beer, so not really wasted. Not very different than growing the same crops for eating. Disclaimer: My knowledge of this area is limited to beers, wines and meads. I cannot claim any knowledge of distillation, nor the degree of wastage involved.
When I make beer there is water pushed through the heat exchanger for the cold crash at the end. But all that water is reused in the garden which I was going to do anyway. In a large commercial operation that water is constantly recycled or a glycol system is used instead so not much wastage. The waste heat from one boil stage can be reused to heat the water for another mash stage too (not 100% though)
Wine making - practically no waste water
Cider - same as with beer. Actually a little less as none is used in a mash stage.
When I make mead, I do use water, but only to dilute the honey, and again, all goes to the finished product. Have to assume the concern is related to distilled products, and I have no idea what level of water use is required there. (I guess there is some wastage related to cleaning and sanitizing, but really?)
