I gave up soda years ago, well almost. I will treat myself to an orange crush and popcorn when I go to a movie. But at home all I drink is tap water and home made ice coffee, black no sugar.
When I go out I normally just get water. I like water. I like tap water. I don't always like the water when I go out because sometimes there's a chlorine aftertaste. I'm also not a fan of hot coffee unless you add lots of cream, and I'm trying to watch my calories / carbs.
I tried cold brew for a while, and frankly found it too much work, now I just brew about 4 tablespoons or 2 ounces of what ever Ground Dark Roast that's in my freezer with about 12 cups of water.
Once it's brewed I turn off the coffee maker and let it sit for an hour or more, and then transfer it to an open top glass pitcher in the refrigerator. I also keep my tap water in an open top glass pitcher in the refrigerator. I like the taste better if I let it breath.
So now I have two pitchers in the frig, one with cold black coffee and one with cold tap water. When I want a drink sometimes I get coffee, sometimes I get water, but very often I will add a splash of coffee to a glass of water, making it flavored water. I never measure, but if I had to guess I would say I add an ounce or two of chilled ice coffee to 12 to 16 ounces of chilled water at the most.
I like the flavor just a splash gives the water. I never feel like I've been cheated with watered down coffee, if anything I like that my 12 cups will last longer.
I also keep chilled salsa bottles of coffee, water, and / or premixed coffee-water in the frig for quick travel options.
Now the math, 8 ounces of cold black coffee has only 2 calories, so 1 or 2 ounces is like zero, or close enough.
Note: Whenever I've tried taking hot coffee and pouring it over ice, black no sugar, its awful. But when I brew it, let it sit, and then chill it overnight I love it.
If you like to mess with your friend's heads, you can take a bottle of chilled lightly flavored coffee water out of the frig, and offer it to them, telling them that its Ice Cold Tap Water, and then take a big long drink before admitting that it's really ice coffee.