For the first three plagues – Blood, Frogs, and Lice – it was Aharon who hit the water and hit the sand with the Staff of Hashem, thereby bringing on these plagues. Chazal say that Moshe Rabbeinu owed Hakaras HaTov (gratitude) to the water which saved him as an infant, when the basket his mother hid him in floated in the Nile River. Likewise, it was the sand that saved Moshe when he buried there in the Egyptian whom he killed. Moshe “owed” so to speak to the water and the sand and therefore did not want to be the initiator of a plague which came from these entities.
We are all aware that water and sand are inanimate objects who don’t appreciate a ‘Thank-you’ and don’t even know what a ‘Thank-you’ is. And yet, we see that a person needs to have Hakaras HaTov even to inanimate objects. So clearly, Hakaras HaTov is not for the benefit of the person (or object) receiving the Hakaras HaTov. It is for the benefit of the person who gives the Hakaras HaTov. If a person learns to show gratitude even to something like a rock or sand or water, then he will certainly show Hakaras HaTov to a human being.
I recently heard the following story: Rav Shlomo Zalman Auerbach was once in the hospital. He made a point of thanking every doctor and every nurse for the care they provided for him while he was in the hospital. (This is something that someone does not need to be Rav Shlomo Zalman to do. Many people rightly have this practice under similar circumstances.) But then he asked if he could see the woman who went from room to room to water the plants in the hospital rooms. He said that the plants brightened up the room and therefore the woman who poured the water into the plants to make sure that they would stay fresh also needed to be thanked for her efforts.
Most people may thank a doctor or a nurse who was helpful to them. But thinking about the lowly woman that goes from floor to floor and from room to room watering plants? She also should receive Hakaros HaTov, because if even inanimate objects receive Hakaros HaTov, certainly every human being deserves no less.
