CANON II.-If any one saith, that true and natural water is not of necessity for baptism, and, on that account, wrests, to some sort of metaphor, those words of our Lord Jesus Christ; Unless a man be born again of water and the Holy Ghost; let him be anathema.
Though in this case, God which hath not bound his grace, in respect of his own freedom, to any Sacrament, may and doth accept them as baptized, which either are martyred before they could be baptized, or else depart this life with vow and desire to have that Sacrament, but by some remediless necessity could not obtain it. Lastly, it is proved that this Sacrament giveth grace ex opere operator, that is, of the work itself (which all Protestants deny) because it so breedeth our spiritual life in God, as our carnal birth giveth the life of the world.
Rheims contradicts himself, and Trent's canon. He says water is necessary, then says it's not.
If God "accepts them as baptized," and they are saved, then baptism retains its necessity.
Trent does not support this ideal. In fact, it condemns it, by stating that 1) baptism is necessary and 2) water is essential to baptism.
Thus, water baptism is necessary for salvation. BOD just provides grace/justification.