Definition of flat water in English:

flat water

Syllabification: flat wa·ter

noun

Ordinary tap or bottled drinking water, as opposed to sparkling water: you won’t get flat water here unless you request it
More example sentences
  • There are plenty of things you can do to flat water to make it more fun.
  • Carbonated water, like Perrier, is another alternative to flat water.
  • Of course the people who really know aren't going to be in the bar, they're in a dank meeting room drinking flat water and sucking on those boiled sweets you find only in hotel meeting rooms.