To be fair its not just a feature of ryans or that aircraft type.
All aircraft will get it forming on the hull where you can't see it. Usually they have valves at the bottom of the hull which open at somepoint after landing which vents the condersate which has melted and run down into the belly.
Which is why you sometimes see patches of water under the aircraft on a dry ramp on stand.
It is quite a common question from new ramp handelers what the patches are.
Usually we wait until they have stuck thier finger in the puddle to see if its oil/fuel before we kid them on its overflow from the toilets before telling them the truth.