Shifted atoms

The atoms of the water turned because of the charge of the rod. The positive charges are attracted by the negatively charged rod, whereas the negative charges are repelled by it.

This is a special form of Induction.
If you now think about the force which is acting from the charged rod on the aligned positive and negative charges of the water, you are very close to the solution of the exercise.

If you have become curious now and the drawing was fun to you, you can also do a bonus task on inducation.