In a medium-sized pot, combine water, sugar, rice vinegar, and kosher salt. Bring to a boil.
Once boiling, remove from heat and let the mixture cool for 10 minutes.
Prepare a large airtight container for pickling.
Add the sliced radish, cucumbers, and matchstick carrots to the container.
Pour the cooled liquid mixture over the veggies in the container.
Close the container tightly and let the veggies marinate in the refrigerator for at least 1 hour before using in a dish.
