The gardener_______(water) the lawn if we tell him.

If you haven't told him yet, then that verb must be in the future tense, right?

What is the future tense of "water"?

waters

water

The missing word in the sentence is "will water".

To identify the missing word, we can use the structure of the sentence and the context. In this case, the sentence is in the present simple tense and talks about a possible future action.

To form the future tense in English, we often use the modal verb "will" followed by the base form of the main verb. In this sentence, the main verb is "water". Thus, "will water" is the correct form of the verb.

If we tell the gardener, he will water the lawn.