Place almonds or cashews in a glass bowl and add enough distilled water (nor the mineral water) to cover them by at least a centimetre. Cover the bowl with a kitchen towel and refrigerate overnight.
Drain and rinse nuts well, discarding soaking liquid.
Place nuts in a food processor and blend along with the 650ml of fresh mineral water.
At this stage, you can add some flavouring such as honey, agave syrup, Medjool dates, vanilla extract or cocoa powder to the blender. Slowly work up to the highest speed then blend for two minutes.
Pour mixture into a strainer lined with muslin cloth (cheesecloth) and allow the liquid to drain through the solids. Gently squeeze the cheesecloth to extract more liquid.
Keep refrigerated and drink within 2-3 days.