Loosened the fitting for that line inside the salt tank and it is water under pressure.
Unless the unit is in the BRINE FILL cycle, there should be no pressure on that fitting, I believe. During brine draw, it sucks from the brine tank thru the valve into the resin, and in brine fill, it is pressurized because it is filling the sat tank with water. All other times, I think it should be static...