My speedometer is ~95% full of water. I assume that unlike a compass that this is unintentional? How would water be getting into this (and how do I get it out)? as the top center gauge I could see it first in line to catch drips, but I have not yet found anywhere that water could have crept in?

If it is a pitot tube style speedometer than I would say it has an internal water leak. I am assuming this is the case. Buy a GPS model.

I believe the liquid is supposed to be there, my tantrum has a liquid filled gaffrig speedo.

They were the hot ticket, when I still had hair, now they're like 8 tracks!

They are purposely filled with glycerin to prevent needle bounce. They have a little bit of air in them for expansion.

Without knowing the Make and Model (year would help too) of the speedo , picture would be even better , there is no generic answer to the question .
I have two speedos in two different boats that if they had water in them they would have to be replaced . In that instance a perforated pressure sensing diaphram would be suspected.
However , some other speedos , namely the higher end models , do have what looks like water in them and it's supposed to be there . .
So exactly what are you dealing with ?

Oh, I thought a liquid speedo was like when my buddy opens a beer right as i'm coming on plane. If it stays in the can, you're not going fast. If it sprays out everywhere, you're going fast.

The dash is soggy/ leaking and the float switch in the speedo is broken.

My 96 scarab had a liquid filled speedo.