Final answer:
The correct form of tener que is tiene que. It is used to indicate obligation or necessity.
Step-by-step explanation:
The correct form of tener que to fill in the blanks with is tiene que. So the sentence should be: El perro tiene que beber agua.
Tener que is a Spanish expression that is used to indicate obligation or necessity. In this case, it means 'has to' or 'must' in English. It is followed by the infinitive form of the verb that expresses the action that needs to be done.
For example, 'tener que estudiar' means 'have to study', 'tener que comer' means 'have to eat', and so on.
Learn more about Spanish grammar