Mix the coffee and the water. Leave it on the counter overnight. Strain in the morning, preferably through cheesecloth.
For hot coffee just add hot water to taste to 1/4 cup (or more) of the concentrate mixture (depending on how strong - or not - you like your coffee). 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.