Puree the strawberries in a food processor or a blender. Add it to a half-gallon jar or large bowl. Juice the lemons with a lemon juicer and add to the strawberry puree.
Add the sugar and stir until it’s completely dissolved into the fresh lemon juice with strawberry puree. Then, pour in the cool water and mix well.
Next, stir in your fermentation starter to the sugar water—this can be whey, a ginger bug, or water kefir.
Drop a couple of raisins into the bottom of your fliptop bottles, then pour the mixture into the bottles. Seal them tightly. Allow the mixture to ferment at room temperature for about 72 hours. You can also keep it in a sealed half-gallon mason jar, leaving about 1 inch of headspace. Either way, when a raisin rises to the surface, it's a good indicator that your strawberry lemonade is ready.
Refrigerate the bottles overnight. Before serving, remove and discard the raisins (if used). Pour your lemonade through a fine mesh strainer, then enjoy your naturally fermented homemade lemonade!