Use this recipe, adapted from a recipe in Commander's Kitchen cookbook, to make a big batch to last up to a month in the refrigerator.
Stir together ground coffee and 3 1/2 quarts cold water in a 1 gallon pitcher until all ground coffee is wet; let stand 12 hours at room temperature.
Pour coffee mixture through a large, fine wire-mesh strainer, discarding grounds. Clean strainer; place a coffee filter or double layer of cheesecloth in strainer, and pour coffee mixture through lined strainer. Return coffee concentrate mixture to pitcher; cover and chill up to 1 month.
Note: To make iced coffee, stir together 1/4 cup each of Coffee Concentrate and water. If desired, stir in milk and sugar. Serve over ice.