Combine the water and cashews and let them soak for 8 hours or overnight. Cashew nuts may develop a slight purplish discolouration. This is normal and not a sign of spoilage.
Drain the cashews and add them to a blender. If your blender is not strong, I recommend chopping up your cashews before putting them in the blender. Add in the lemon or lime juice.
Choose the flavour combination you like, and put those ingredients into the blender.
Pulse until a nice paste forms. You may need to stop the blender occasionally, and use a spatula to push down the sides, so that everything is smooth and well combined.
Using a spatula, transfer the paste into a small container. Be sure to push out any air bubbles. The cashew spread will be thinner in texture and have a very nutty flavour. Leave the cashew spread on the counter at room temperature, and ferment for up to 48 hours if you would like the spread to have a more sour taste.
You can also just place the spread directly into the fridge. It will keep for about 2-3 weeks, and will become denser. It will develop a more "cheese-like" flavour as it ferments.