Place coffee grounds in the center of the paper coffee filter. Gather the top of the filter to make a pouch with the coffee grounds secure inside the pouch. Close the top of the pouch by tying the top of the pouch with kitchen string.
Fill mason jar with water and place the tied coffee pouch in the jar, making sure it is submerged in the water.
Put a lid on the jar and refrigerate for 12-24 hours. The longer the coffee steeps, the darker and richer the coffee flavor.