Prep the berries. Rinse everything thoroughly. Slice the strawberries so more surface area touches the water. Leave blueberries and raspberries whole for a cleaner look, or lightly press them with the back of a spoon for faster infusion.
Build the base. Add berries, citrus slices, and mint to a large mason jar or pitcher. Pour in the still water. Give it a gentle stir so the flavors begin mingling like networking pros.
Let it infuse. Cover and chill for 30–90 minutes. Thirty minutes gives you light, fresh notes; 90 minutes delivers fuller fruit flavor. Longer than 12 hours? You'll start flirting with mushy berries, so set a timer.
Add the bubbles. Right before serving, pour in the sparkling water. Stir once—gently—so you don't knock out all the carbonation like a rookie.
Serve smart. Fill glasses with ice, strain the infused water over, and add a few berries for looks. Taste and adjust: more citrus for brightness, more mint for aroma, or an extra splash of sparkling water if you want extra fizz.
Scale it. For a party pitcher: triple everything and add the sparkling water in batches so it stays lively. For grab-and-go: make individual jars, then top with sparkling water just before drinking.