In a medium bowl, combine the lemon juice and water. Place the eggplant slices into the lemon water to soak while you bring a saucepan of lightly salted water to a boil. Drain and rinse the eggplant slices, then place them into the boiling water. Cook for 8 minutes or until barely tender. Drain.
Preheat the oven to 180 degrees C. Lightly grease a 2 litre casserole dish. Layer the eggplant slices, tomatoes and onion in the dish, sprinkling each layer with a little flour as you go.
In a medium bowl, stir together the sour cream, garlic, salt and pepper. Spread this over the top of the casserole. Sprinkle generously with paprika.
Bake for 45 minutes in the preheated oven until the top is nicely browned and there is a bubbly sauce.