I recently bought a used John Deere 790. The tires were filled with liquid which the owner said was water. I emptied some of it and it indeed looks like dirty water. To me this would ruin the rims. What should I do?
If your tyres have tubes in then it won't be a problem.
How cold does it get where you are? Water ballast can freeze if it gets cold enough.
I was warm (-5 Celcius)enough not to have freezing issues on mine.
In WA I would be hard pressed to not run some type of antifreeze in the rear tires. I suggest - have the "liquid" tested. If it is plain water - drain - reinstall RV antifreeze, RimGuard, methanol or the like.