Put the peaches, sugar, and water in a large pot and bring to a boil. Reduce to a simmer about 15-20 minutes.
Squish the peaches in the pot (I use a potato masher), and pour this mixture through a fine-mesh strainer into a large bowl.
Add the vanilla extract and whey to the mixture in the bowl and stir. Once combined, pour into flip top bottles and set in a warm area of your home.
After a couple of days, you can open a bottle to check for taste and let the fermented gasses out so it doesn't build up too much. Fermentation can take anywhere from 2 days to a week. Move the bottles to the fridge once they are ready.
How to get whey - Just scoop a container of plain whole yogurt into a dishtowel, tie it up onto a cupboard door and let it drip into a jar - the liquid dripped off is probiotic rich whey! The leftover yogurt in the towel is like Greek yogurt or cream cheese - yum! For dairy-free version - use 1/2 cup water kefir or kombucha in place of the whey.