Which number should replace the question mark?

After several exciting dates, Jim invited Tina over to his house for a home-cooked dinner.
When she sat down at the table, she noticed that the dishes were the dirtiest that she had ever seen in her life.
"Have these dishes ever been washed?" Tina asked, running her fingers over the grit and grime.
Jim replied, "They're as clean as soap and water could get them."
Tina felt a bit apprehensive, but started eating. It was really delicious and she said so, despite the dirty dishes.
When dinner was over, Jim took the dishes outside, whistled and yelled, "Here, Soap! Here, Water!"