Yet placed in perspective, that 1 ppm copper on top off or replacement likely not going to impact overall system. Copper does exist in NSW and so does phospate yet I doubt most systems have 1 ppm copper existing as 100% off that filter no longer being 100%.
Using replacement water with 1ppm copper will most certainly lead to issues. 1 ppm itself is very high for copper and much much higher than NSW levels. Worse though it would build up in the system as it wont evaporate and to my understanding it wont be utilized by anything in a reef tank as fast as people need to topoff. Even when treating ick it is usually only at 2-2.5 ppm so clearly even very low levels can have significant impact.
Having said that though i do agree if your rodi is 1ppm of something...then its not very likely it has much if any copper in it. I feel perfectly safe using tds in single digits myself.