How would you confirm that a colourless liquid given to you is pure water?

Due to the anomalous expansion of water; ice on the top of the water freezes whereas the deeper layer remains warm. This heat is not able to escape into the atmosphere, thus protecting the fish and other aquatic animals from the future cold. Ice is itself cold but preserves the heat within. Similarly, our parents do so much for us, without expecting anything from us.  

How can you do something for your parents?

1. By studying and getting good marks.
2. By cheating them.