U need to first select fifteen families having the same number of members.So that the comparison is appropriate.Then, find out what is their daily water usgae. Fill that data in the USAGE column. Now, out of that usage, find out how much water does the family waste. Fill that data in the WASTAGE column. The comparison and tablemaking is done. Now to make a bar graph, u need to make a double bar graph of the usage and wastage of each family. You can refer to the kmage for the same.The given bar graph in the image is of favourite icecream vanilla or choclate among children of different grades(std. Similarly you can make usage and wastage graph among fifteen families. Hope this will help you.