First bring the water and the salt to a boil.
Once it’s boiling add the tapioca pearls. Now turn down the heat and let this simmer until the pearls are see though. Stir it every now and then to prevent it from burning. Then spread it on a silicon sheet and let it dry at 60 degrees Celsius. After that fry them at 210 degrees Celsius and then season then with salt. Be careful with the frying process because the oil is really hot and the tapioca will puff very fast making the oil splash.
You can also flavor your water to give the crisp a specific taste. Try it with a dashi broth, a ginger broth or maybe a smoked pork broth. If you can think it, you can create it. Just be aware that the liquid doesn't contain much sugar otherwise it will burn when you fry it.