The silicon is isolated from sand, from a recipe that leaves it in a powder form in the bottom of a container of water. I actually haven't tried this out yet, but I plan to when I get some proper materials. I just wanted to see how I could use silicon before I isolated it.
I looked at the website, and thanks! It appears I could use silicon for water filtration. I still am wondering whether I could make some silicone with it, though; as I have heard it is useful for a number of things.