Place the water and kombu in a pot over low heat. When the liquid comes to a simmer, turn off the heat and add the bonito flakes, stirring to infuse it fully into the broth. Allow it to sit for 5 – 10 minutes, then strain, discarding the solids or use them to make a second running’s dashi and repeat the process. Cooled dashi will last in the refrigerator for up to a week.