still water; хим. carbon dioxide-free water

https://www.reddit.com/r/gifs/comments/3eepxs/would_you_prefer_your_water_bubbly_or_flat/

Я тоже то же говорю — flat water is too flat / and I'm not too high / to drink it!

And, besides, that bubbly water isn't bubbling away as it was discussed earlier.

Exactly!