Which of the following sentences is correct?
In the table, water usage in Brazil and America is compared.
In the table, water usage in Brazil and America are compared.
Is compared. The subject is water usage, not America nor Brazil.
In the table, water usage in Brazil and America is compared
According to this source, if subjects are joined by "and", you determine the number of the verb by the following procedure: Split up the sentence into two and assess whether the meaning is still the same. If this is the case, the verb has to plural. Otherwise, it is singular.
For the sentence to be "are compared" we'd need
In the table, water usage in Brazil is compared.
In the table, warter usage in America is compared.
each to be senseful on their own, which they aren't. Therefore, we need a singular verb.