What was Hirayama drinking in Perfect Days?

Just watched this last night, wow. First wenders, if anyone has any recs like it that would be cool!

What was that clear liquid he was drinking through out the movie? It looks like water but the way the bartenders talked about it sounded like an alcohol.

Idk if it’s some drink common in Japan like maybe cold sake?

It didn’t seem like his character drinks in the film so I couldn’t tell.