Ananias was a Jewish believer. All the Jews initially saw Christianity as a spur off of Judaism. As a result, they believed that all the traditions and rituals of Judaism still applied.
WaterBaptism was not invented by John the Baptist. Water purification rites are part and parcel of Judaism and John^s message was twofold: -> repentance from sin (departure from God) -> the impending advent of the Messiah
It was not until Paul received the revelation of salvation by GraceThroughFaith that it became clear that Judaism was no longer a valid way to approach God.
Once Paul began to preach the Gospel to Gentiles not requiring them to become proselyte Jews, there was a division between the Jewish church, led by Peter, and the Gentile church, led by Paul.
A council was held to decide what legalism from Judaism should be imposed upon Gentile believers. They settled on these abstainances: -> from things offered to idols -> from blood -> from things stangled -> from fornication
So, Ananias was only telling Paul what the Jewish believers felt was necessary. If you think about it, it is obvious that physical water could not wash away spiritual sins.
^What can wash away my sins? Nothing but the blood of Jesus.^
What Ananias believed and what Peter originally taught was not GospelTruth. Paul received the revelation of GospelTruth and it made clear that Judaism was the old cloth and the old bottle into which the new cloth and new wine of Christ Jesus should not be sown or poured Mar 2:21,22.