Rev 17:15. Then he said to me,”The waters which you saw, where the harlot sits, are peoples, multitudes, nations and tongues.”
What do many waters mean in the book of Revelation?
Rev 1:15. His voice as the sound of many waters. (Refers to the voice of Christ in heaven).
Rev 14:2. And I heard a voice from heaven, like the voice of many waters, and like the voice of loud thunder. And I heard the sound of harpists playing their harps. (Refers to the 144,000 voices in heaven singing a new song verse 3).
Rev 17:1. Come I will show the judgment of the great harlot who sits on many waters.
Rev 17:15. The waters which you saw, where the harlot sits, are peoples, multitudes, nations and tongues. (These people are related to one voice of praise and worship to the fallen church worldwide, which is opposite to the voices of the 144,000 who keep the Ten Commandments of God and the faith of Jesus Christ Rev 14:12).
Rev 19:6. And I heard, as it were, the voice of a great multitude, as the sound of many waters and as the sound of mighty thunder, saying, Alleluia! For the Lord God Omnipotent reigns.
Conclusion
Many waters are related to the voice of Christ up in heaven and the 144,000 up in heaven. Many waters are also related to the 144,000 singing a new song and the voice of the great multitude praising God in heaven. They also keep the Ten Commandments of God and the true faith of Jesus Christ. These commandments include the Sabbath day which is on a Saturday.
As regards to the harlot sitting on many waters, this represents the worldwide fallen church singing and praising God through false worship and teachings they have received from the scarlet beast. These teachings represent the wine of her fornication in Rev 17:2.3. These teachings are opposite to the Ten Commandments of God and the true faith in Jesus Christ. i.e. the sabbath day which is on a Sunday.