In a large mixing bowl, combine sour cream and mayonnaise until smooth and well blended.
Stir in the dry vegetable soup mix until evenly incorporated.
Add the thawed and thoroughly drained spinach to the mixture.
Fold in the chopped water chestnuts and green onions, mixing until all ingredients are evenly distributed.
Cover the bowl with plastic wrap and refrigerate for at least 6 hours or overnight to allow flavors to develop and meld together.
When ready to serve, cut the top off the sourdough bread loaf and hollow out the center, leaving about a 1-inch shell.
Cube the removed bread pieces to use as dippers alongside your dip.
Fill the bread bowl with the chilled spinach dip mixture.
Arrange bread cubes, crackers, and fresh vegetables around the bread bowl for a beautiful presentation.