Can artificially flavored water be as healthy as regular water?

My boyfriend drinks ONLY flavored water because it's the only sparkling water at home.

At my suggestion, which even provided evidence from the internet, he bought "healthier" flavored water from "Rheinfels Quelle." According to the internet and reviews, it's 100% healthy, meaning it contains no harmful ingredients.

Producing the flavored water himself, which would be healthier, is too time-consuming for him and is therefore not a solution.

But can store-bought flavored water really be healthier than regular water?

I'm just worried because he really never drinks regular water and also drinks a lot of Spezi, Red Bull, whatever.