Step 1 In a medium stockpot, combine 8 cups of water with the konbu and set the mixture aside to steep for 30 minutes. Place the stockpot over medium heat and bring it to a boil. Remove and discard the konbu, and stir in the remaining 2 tablespoons of water. Add the bonito and stir it once to combine. As soon as the liquid boils again, reduce the heat to low and simmer for 5 minutes. Remove any scum that appears on the surface, as this can adversely affect the flavor.
Step 2 Remove from the heat and set aside to steep for 15 minutes. Strain the liquid through a fine sieve or cheesecloth; don't squeeze the bonito flakes. Discard the bonito flakes. This should make 4 to 5 cups dashi.