I read on another thread that you must be vigilant regarding the water in an unpressurized system. Are you talking about the water in the tank, or the system water? If the former, it seems curious, as the dealer I bought my Tarm from recommended sealing the tank. Mine is not sealed, and I have a cover on a pulley for easy access. I added baking soda in the beginning, but I'm in my 5th or 6th season without doing anything more than adding water occasionally.