How am I supposed to know that you want mass instead of weight here?
Hard to say, what should be accepted, but "hmotnost" is the official name of the physical quantity (with kg as one of the basic units of the SI system), "váha" is colloquial. The same holds for "mass" and "weight".
I asked a native, he said the word order is wrong if it's just this sentence alone.
In Czech, this arrangement is possible, but it's as if Yoda said it. :D
Better is: "Známe hmotnost tří litrů vody."
That is the neutral word order. Not a better order in any objective sense.