Mix the ground coffee with the water in a large container. Cover and allow to sit at room temperature for at least 12 hours or up to 24 hours.
Line a fine mesh strainer with cheesecloth and set over a pitcher or other container. Pour the coffee/water mixture through the strainer, allowing all the liquid to run through. Discard the grounds.
Place the coffee liquid in the fridge and allow to cool. Use as needed.
To make iced coffee, pack a glass full of ice cubes. Fill the glass 2/3 full with coffee liquid. Add a healthy splash of half-and-half. Add 2 to 3 tablespoons of sweetened condensed milk (you can use plain sugar instead) and stir to combine. Taste and adjust half-and-half and/or sweetened condensed milk as needed.