Pour the water into a deep stockpot and bring to a boil. Turn down the heat to medium-high and add the kombu and bonito flakes.
Cook the dashi stock for 20 minutes. Place a fine mesh strainer over a bowl, and pour the dashi through the strainer. Discard the kombu and bonito flakes.
Pour the dashi stock into a container and let cool to room temperature, then cover and refrigerate until ready to use.
We add more Kombu and Bonito Flakes than other recipes because we prefer a stronger flavor in the finished Dashi, but adjust the water, kombu and bonito to your liking. The dashi will keep covered and refrigerated for up to one week.