> The density of Titan is consistent with a body that is about 60% rock and 40% water.

That's extremely misleading.

First, rocks have different densities. Sandstone weighs 2g/cc, basalt weighs 3g/cc, so a density "consistent with" 50% basalt, 50% water would be equally consistent with 100% sandstone, not to mention the possibilities of rocks with drastically different densities such as pumice or iron.

Secondly, we are pretty certain Titan has large quantities of liquid methane and/or ethane (check the same Wikipedia link) which certainly account for some of the difference in density between Titan and other rocky bodies.

So yes, there is water on Titan, but it's about as likely to be 40% water as it is to be 40% cheese or 40% iPhones, even if its density suggests a makeup consistent with that.