Here's an activity that I use when we discuss the percentages of water and land on the earth and when we discuss water content of the human body and the foods we eat. I bring in a slice of bread, a carrot, an apple, popped popcorn, a potato, celery, an orange and a banana. We make a 7-column chart to record our data. The column headings include food, estimated and actual fresh weight, estimated and actual dried weight, difference and percentage of water. We estimate, weigh, slice, dry and re-weigh each food. Lastly, We graph the fresh and dried weights on a bar or line graph and the students write a summary of their findings.