Pour in broth, water, and corn, and bring to a boil. (You can cover the pot to make it boil more quickly.) Meanwhile, stir soy sauce and cornstarch together with a fork until smooth.
When broth is boiling, stir in soy sauce mixture. Next, slowly pour beaten eggs into boiling soup, stirring constantly with a fork.
Add spinach, and simmer about 5 minutes until spinach is thoroughly wilted. Taste soup before serving, and add 1-2 tsp. of soy sauce and sriracha if desired.