Place the hazelnuts in a bowl or blender container. Add the water, and allow the hazelnuts to soak, for at least  8 hours, or overnight.

The next morning, drain and rinse well.

Add the drained and rinsed hazelnuts to a blender along with fresh (and filtered) water. Blend until smooth, about 1-2 minutes.

Strain using a nutmilk bag. Hazelnut milk keeps in the fridge for up to 3 days.