*I usually use onion skins and ends, garlic skins, leek ends, carrot peels and tops, celery ends, wilted greens, soft (too soft for regular consumption) tomatoes, zucchini peels, mushroom stems, cabbage core, etc ... any vegetable scraps I accumulate throughout the week, really.
**Some of the water will evaporate during cooking. I started with 10 cups filtered water and ended up with 8 cups vegetable broth.