[header] How to make coffee soda [title] Pour your coffee grounds and water in a large container. [step] Keep in mind that you'll need to make your cold brew coffee the day before you want to make your coffee soda, because it needs to sit overnight. Add the grounds to your large container, and then pour the water in over them. 
Stir your mixture, and then pop it in the fridge. [substeps] The quality of water can make a difference.