Place the thawed spinach in a colander. Squeeze it in a clean kitchen towel until very dry, breaking up any tight clumps.

Stir the sour cream, mayonnaise, and dry vegetable soup mix together in a large bowl until evenly blended.

Add the dry spinach, chopped water chestnuts, and green onions. Fold until the spinach is evenly distributed and no pale streaks remain.

Cover and refrigerate for at least 2 hours so the vegetables soften slightly and the seasoning blooms.

Stir once more, taste, and spoon into a serving bowl. Serve cold with sturdy crackers, bread cubes, or crisp vegetables.