1 c. sour cream
1 c. mayonnaise
2 tbsp. Parmesan cheese
1 pkg. Knorr vegetable soup mix
1 tbsp. finely chopped onion
1 (10 oz.) pkg. frozen chopped spinach (uncooked), thawed and drained
1 (8 oz.) can water chestnuts, coarsely chopped

Combine all ingredients and refrigerate overnight.