The man has been charged with premeditated murder, and is being held in custody.
The defendant heard of his sister's alleged infidelity after her husband's relatives sent the bride back to her family, saying they had seen an unknown man leave her room.
When the girl arrived back at the family home, she was interrogated and severely beaten. Her parents and one other brother have been ordered to spend 14 days in jail for the abuse.
After the interrogation, the defendant reportedly told his sister he was taking her back to her husband, but instead took her out to sea in a boat, pushed her into the water about 50 km from Jordan's capital Amman, and left her to drown.
Soon afterwards, he admitted to police that he had killed his sister, saying he was saving the honor of his family.
Honor killings are relatively common in Jordan. Last month, a court in the country sentenced a man to just six months in jail for killing his 16-year-old daughter. The father beat and then electrocuted the girl in late 2006 after hearing she had cheated on her new husband.
