Blend flax seeds and water in a blender on high for 1 minute; allow to rest for 2 minutes. Blend again on high for 1 minute; allow to rest for 5 minutes. Blend again for 30 seconds.
Pour milk through a nut bag or a strainer lined with cheesecloth into a pitcher or glass container; press solids with back of a spoon to extract liquid. Gather cheesecloth around solids; twist and squeeze to extract all the liquid.