The Eunuch believed God's testimony concerning the resurrection, ascension, and intercession of Christ. As Philip required such faith from the Eunuch before he was baptized, God's ministers must require the same of you. If the Eunuch had not believed, he would not have been baptized. If men were not prejudicial by human opinion and religious tradition this question would be redundant. Immersion is not a mode of baptism.
Immersion is baptism, without it there is no baptism.
Paul speaks of baptism as a burial. When you bury a corpse in the earth, you do not throw a few grains of sand in his face. You put him beneath the ground. And a man is not buried in baptism by sprinkling a few drops of water in his face. He must be immersed in water.