Pour ground coffee in a large heat proof bowl or pot. Add in 8 cups boiling hot water. Stir to get all of the coffee grounds wet then let it sit 5 minutes.
Note: (If grinding your own coffee, don't grind it too fine or it will go right through your cheese cloth).
If you have a french press, put it through the press in a couple batches, otherwise, Place the colander over a clean, heat proof bowl or jug and line the sieve with 6 layers of cheesecloth (this will catch the stray coffee grounds).
After the coffee is all strained, discard the coffee grounds and add in 8 cups ice cold water to the coffee. Refrigerate until ready to use. This concentrate lasts 3 weeks to a month in the fridge.
To serve, fill a tall glass or mason jar almost to the top with ice. Pour your coffee concentrate to the top of the ice.
Add 1-2 tbsp sweetened condensed milk depending on how much of a sweet tooth you've got. Stir with a spoon until the condensed milk is well incorporated (it tends to sink to the bottom).