I also only use NSW and have had no problems. I always ensure I collect froma clean area unpolluted by nearby seafaring traffic or harbours. I fetch water before a water change but usually there is enough for two, so sometimes keep the water for a week. Also store it in a dark sealed container. There definitely is some die off, but so long as you keep the inputs to your system minor (small changes) I do not think it will pose a problem. As has been mentioned before I would make the change as gradually as possible. I am not sure of what the exact chemical composition in the water, but it is sure to have some nuances.
