Add 2 g kanten powder and 15 g granulated sugar to a cold saucepan and mix them together.
Add 500 ml water to the pan and whisk.
Place the sauce pan on the stove and bring to boil over medium heat while stirring continuously. Use a silicone spatula to scrape the bottom of the pot. Once it's boiling, set a timer for 2 minutes and keep stirring until the time is up.
After two minutes, reduce the heat to low and add 400 g smooth red bean paste one-quarter at a time while mixing constantly. Make sure the mixture is smooth with no lumps before adding the next quarter.
Once the koshian has melted and incorporated into the mixture, add 1 pinch salt and turn off the heat. Continue to mix for 1 minute to help release the heat.
Pour the mixture into molds or a Japanese "nagashikan" tray and leave to cool to room temperature (approx 20 mins).
Once cool, cover and transfer to the refrigerator. Chill for 30 mins or until fully set.
Carefully remove the mizu yokan from the mold and cut into equal pieces.
Serve and enjoy!