If your family eats canned fruit
odds are good that the liquid that's left after you eat the fruit is sugar water. (On store-bought cans, the label will specify the fruit has been canned in "light syrup" or "heavy syrup." That's code for sugar water.)
If you add a squirt of this
you will end up with a nice cold glass of subtly fruity lemonade.
And what could be more frugal?
(Oh. And feel free to add more water if it's too sweet, or more lemon.)