Soak the whole tiger nuts in filtered water overnight (I cover them and keep the container in the fridge).
In the morning, drain the soaking water, add the soaked tiger nuts to a food processor, and process until ground.
Transfer the ground tiger nuts to a blender, top with the 900 ml of filtered water, and blend until it looks like milk. If you have a smaller blender like a Nutribullet, mix the tiger nuts and the water in batches.
Using a nut bag, separate the pulp from the liquid.
Store the milk in a glass bottle, in the refrigerator, for up to one week.