In a saucepan over medium heat, cook the chopped spinach until wilted, about 3 minutes, then transfer to a fine mesh sieve and press to remove excess moisture.

In a mixing bowl, combine the sour cream, softened cream cheese, and mayonnaise, stirring until smooth.

Add the garlic powder, onion powder, salt, and black pepper to the creamy mixture and stir to combine evenly.

Fold the drained spinach into the seasoned cream base until evenly distributed.

If using, fold in the chopped water chestnuts and green onions to add crunch and freshness.

Cover the bowl and refrigerate the dip for at least 1 hour to allow the flavors to meld.

Transfer the chilled dip to a serving dish and garnish with extra green onions before serving.