Add a half-cup of filtered water to one-and-a-half cups of coffee grounds, stirring gently. Add two more cups of water, agitating the grounds as little as possible. Cover and let steep at room temperature for 12 hours.
Slowly strain the coffee-ground mixture with a paper filter, which will take five to 10 minutes or until all liquid has seeped through. If the coffee looks cloudy, then strain again using a new filter. Store, refrigerated, for up to a week. This is a concentrated brew, so upon serving, dilute it with more filtered water or milk to your liking.