Slice the radish into thin slices and place in a bowl.
In a separate bowl, mix together the water, sugar, and sea salt until dissolved.
Pour the mixture over the radish slices and stir to combine.
Cover the bowl with plastic wrap or a lid and let sit at room temperature for 24-48 hours, stirring occasionally.
After 24-48 hours, transfer the fermented radish slices to an airtight container and store in the refrigerator for up to 2 weeks.
