Normally, the power given to a Saint couldn’t be used entirely.

[...]

If Saints could use such power at 100%, the high pressure would cause the Saint’s body to self-destruct.

[...]

(…Acqua, he doesn’t have the limit of being...a Saint…?…That power…has it already overcome what…a human can already control…?)

Needless to say, besides being a Saint, Acqua had the power of God’s Right Seat. The reason for him to be called Acqua of the Back was because he had the element of the Archangel Power of God. Normally, one would think that it was just a natural addition of power, but in reality, this increased power doubled the burden on him.

Yes.

What was amazing was that Acqua had already controlled 200% of that power and still hadn’t gone amok, his facial expression not changing at all.

Toaru Majutsu no Index vol.16