This is a great way for students to get a feel for what a gallon of water is. First the teacher must explain that astronauts only get to use 6 gallons of water each day. Show the class 6 gallon jugs of water and ask if they could make do with that each day. Weigh a gallon of water and explain that the astronauts can only have so much because it weighs too much. Then have the class list all the ways that they use water everyday: drinking, cooking, flushing the toilet, showering, brushing teeth, washing hands etc. You could also discuss the shape of the container and how it could be made more space efficient. Have students design other containers that could hold 1 gallon of water but be more easily stored.