How a toilet flush works
Look at the water in the tank. When does the water in the tank stop filling? Can you think of ways to fill the tank with less water so that less water is used for flushing?
What is condensed milk?
Look how viscous (thick and sticky) condensed milk is! Think about how quickly it can flow through a hole in a can when it is poured out.
The crow and the pitcher
What property of the pebbles allows the crow to drink the water?