In a small pan over high heat, add the water, soy sauce, sugar, and garlic paste. Stir and cook for 5 minutes.
Take about 2 tablespoons of the sauce and mix it in a separate dish with the cornstarch. Mix until all the cornstarch has dissolved and then add it to the sauce. Cook for 1 minute while stirring.
Let the sauce cool and store it in your fridge. Buen provecho!
Notes
Sweeter version. Just add ¼ more of sugar.
Storage. Make sure to store it in an airtight container, like a jar or bowl, for no more than 1 week. What I like to do is to pour my leftover sauce in a mason jar and freeze for up to 6 months.