The sour was a beverage which was drunk mixed with high alcoholic beverages, especially shochu, rather than being drunk individually, and shochu with sour was called chuhai named after sho-'chu' (shochu) and high sour.
サワーは、それ単独で飲むよりも、高濃度のアルコール飲料、とくに焼酎に加えて飲むもので、焼酎をサワーで割ったものを、焼「酎」とハイサワーに由来してチューハイと呼んだ。