Place the almonds in a medium bowl and cover with purified water by 2 in [5 cm]. Cover and let sit at room temperature for 12 hours. Drain the almonds, then place them in a blender along with the 41/2 cups [1 L] purified water. Blend on high speed until very smooth, about 2 minutes. There will still be some pulp left.Working in two batches, pour the liquid through a fine-mesh strainer set over a small bowl. Using the back of a wooden spoon or ladle, press down on the almond pulp to extract as much of the milk as possible. Discard the pulp, and then repeat with the rest of the liquid. Repeat the straining process as necessary to reach the desired texture. Taste and stir in the vanilla, maple syrup, or salt, if desired.Store in an airtight container in the refrigerator for up to 1 week. Stir before each use.