How effective is liquid water in slowing the velocity of bullets?

the question is asking for  a subjective answer, it is much more effective than air, but it is much less effective than titanium.

The mythbusters series found that supersonic bullets disintegrate on entering water and their energy is almost immediately lost. Subsonic rounds only penetrate a few feet before becoming non lethal

Fairly effective considering it's water.  Faster velocity projectiles will break up after only two - three feet, while slower moving 9mm and slugs can hit as far as eight feet.

Very.