Arian, Jehovah's Witnesses Baptisms Invalid
How come Arian baptisms are valid but Jehovah's Witness baptisms aren't?
Actually, the baptisms of both the ancient Arians and the modern-day Jehovah’s Witnesses (JWs) are invalid, because neither group believed/believes in the divinity of Jesus and the reality of the Trinity. Indeed, the JWs are modern-day Arians.
For more on this topic, see our Catholic Answers tract on Trinitarian Baptism.