Answer:
Step-by-step explanation:
The answer is indeed: The water leak ruined my keyboard.
In the original sentence "My keyboard was ruined by the water leak", we can notice the characteristics of the Passive Voice: the subject of the sentence, "my keyboard", suffers the action represented by the main verb instead of being the one causing/doing the action; there is the auxiliary verb "be" followed by a main verb in the participle, "was ruined"; the agent responsible for the action is preceded by the preposition "by" at the end of the sentence - "by the water leak".
To properly transform this sentence into its Active Voice counterpart, we must make the following changes: the subject now becomes the object of the verb; the auxiliary verb "be" disappears and the main verb is conjugated accordingly; the agent now becomes the subject of the sentence.
Thus: My keyboard was ruined by the water leak = The water leak ruined my keyboard.