distilled water is the purest form of water you can have if you get a good distiller. the problem is the process is boiling off the water passing it through demister pads then recondencing it, this leave behind any impurities as they can not be carried over with the steam. cheeper units will have no demisteres so you might get carry over in the form of water drops which will alow some impurities to be taken to the final water output. they consume a lot of power for the amount of water they make (think about boiling off 5 gal of water with a tea kettle
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we use them in a much larger version (805 gal per hour) but that is because the ship is a steam ship and we just use exhaust steam from the engins to heat the water.
now the coper comes into play because if the condenser is coper you are taking a hot dry steam and cooling it back into water that is verry pure, we all know pure water is a solvent so it will pick up trace elements of copper from the tubing. might not want that in your tank.
Steve
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