If this were to happen (and I don't think it will), then you'd want that water connector to be part of the charging cable to avoid a two step hookup. That requires a new charging cable standard (which is why I don't think it'll happen).

Also, water kinda sucks to deal with for something like this. What if, for example, the water flowing in isn't pure? What if it's hard water? Your battery cooling tubes could need flushing and might start growing nasty fungus and such.