I got this tip form a WW2 children's war effort booklet.
It recommended saving the water from cans of veggies to use as veggie broth.

Ever since, I've kept an empty, clean salad dressing bottle in the fridge and everytime I open a can of veggies, I pour the water form it into this baottle. any time I need broth, I use that, or even plain water in soups, since I don't like keeping the mixed water for more than a week or two, the rest goes in the soup pot.