In a covered jar or French press carafe, cover ground coffee with cold water. Give a stir to make sure all grounds are soaked. Let stand, unrefrigerated, for 12–18 hours.
Strain out coffee grounds through a fine strainer or, if using a French press, press the coffee as you would when making hot coffee. The remaining liquid is a rich coffee concentrate with the same approximate strength as espresso.
Dilute with water for iced coffee, or for a cold-brewed latte, mix concentrate with cold milk.