If you look at it and it looks like water, then it is "real and natural" water. Trent did not say to examine it under an electron microscope or even a magnifying glass.
Aside from that, from the description of the baptism in the OP, the baptism is presumed valid, if there is any doubt at all, then the OP must prove invalidity. That's how that works.
Even if only one drop of water hit the skin and rolled down even a minute fraction while the words were being said, there would be no doubt, in your case, the baptism was valid and you could not prove otherwise.