You can prepare the coconut water kefir in 3 different ways. You can use an existing kefir as a starter, kefir starter culture, or use kefir grains. The cheapest way to prepare it is to use the kefir grains, whether they are milk or water kefir grains.
A Ceylon Cinnamon Stick
7 cups of fresh Coconut Water
5 tablespoons of Water Kefir Grains
Get a half a gallon jar and pour the coconut water inside, then you can add the water kefir grains inside as well and close it but not too tight. Then let the mixture stay for 48 hours, because if you leave it more the fermentation can cause a small explosion.
Once the fermentation process starts the color will become lighter, and you will know that the process is done when the kefir grains will be on top. Then get the grains out of there and you may use them for the same purpose again, if you want to make the process again and make one more batch.