idk if you have well or city water, but I wouldn't trust even treated well water for my frog. In addition to metals that water purifiers might not get out, well water can have CRAZY high bacterial concentrations. I've done lab tests on well samples, and I would seriously worry about it causing infection in a frog with a weak immune system.

Next time you soak your frog support its head or something... If it's got MBD to the point it can't keep its jaw closed and has weak legs that can't hold it up correctly, I'd worry about water getting into its respiratory system.