Get some Bob's Redmill Tapioca Flour and place it on a dish deep enough to accommodate all the flour plus the water. Cover the tapioca with water. The water will bubble as the the tapioca starch starts to absorb it. Wait an hour, or up to overnight, then slowly pour the water out. You'll notice the starch now looks gummy, so we need to dry it.
Using paper towels, or a clean dish towel, press gently against the gummy paste. I do this a few times, exchanging the paper towels for drier ones.
When the gum looks chalky, and can be perforated with a fork, break it into chunks.
Using your hands, break these chunks into a sandy mixture.
Finally, pass that sandy mixture through a strainer to obtain a finer texture.
Store the tapioca gum in a zippy bag, or in a glass container. It should last you 5-10 days in the fridge.