
Use a mandoline slicer to thinly slice the radish into rounds that are about 0.3cm / 0.1 inch in thickness. Place the slices into a sterilized wide-base glass jar.
Combine the water, sugar, vinegar, and salt in a saucepan. Heat over low to medium-low heat, stirring, just until the sugar dissolves (about 2 to 3 minutes). A gentle simmer is fine, but boiling is not necessary.
Pour the brine over the sliced radish and close the lid. Leave the jar at room temperature for 3 to 4 hours then refrigerate. The pickled radish should be ready to eat within 1 to 2 days.
Serve chilled with your favorite meal (e.g. Korean BBQ pork). It can be refrigerated in an air tight container for several weeks.