Since we discovered that my daughter was aspirating thin fluids, we make up several cups at a time of this tapioca thickening base and add it to all kinds of things. We mix it about half and half for the child with aspiration issues, and it helps to keep whatever she drinks from ending up in her lungs.
You can expect to see more recipes featuring this base soon--it makes a nice substitute for milk and other thickening/smoothing agents in smoothies and other beverages.
Mix 1 tablespoon tapioca starch per 1 cup of cold water.
Heat, stirring frequently, until almost or just barely boiling. If cooking on the stovetop it may be a bit smoother as you can stir it more constantly, but I usually do it in the microwave. In the microwave I start off with 1 minute, then continue cooking in 30-second increments, stirring well at each pause.
The mixture will thicken and become more transparent-looking (less like white powder mixed into water, and more like a cohesive whole). Stop cooking it at that point, or it will begin to separate again.
You can store this in the refrigerator and mix it with other fluids to thicken them without needing to reheat it. If it gets lumpy, put it in the blender and it will become smoother but slightly less thick.