en_tn_condensed/rev/16/05.md

the angel of the waters

Possible meanings are 1) this refers to the third angel who was in charge of pouring out God's wrath on the rivers and springs of water or 2) this was another angel who was in charge of all the waters.

You are righteous

"You" refers to God. (See: rc://en/ta/man/translate/figs-you)

the one who is and who was

"God who is and who was." See how you translated a similar phrase in Revelation 1:4.