Okay, better way to concentrate ferrous solutes from tap water:
1. use a conic separation funnel with a good stopcock ($30.45 USD at Amazon).
2. Fill with your tap water and mount at least one good neodymium magnet near the bottom .
3. Leave the stopcock closed and let the water evaporate out the top.
4. Refill as desired until complete, and again at the very last time of the period.
5. You will get higher concentrations of all dissolved salts that occur at the outflow of your water treatment plant. I do not know the ambient water hardness figures in Sydney, but it surely cannot be worse than the waters here in the far upper Sacramento River valley area (Redding).
I think you will get reagent contamination primarily from Mg and Cu salts. The copper is most concerning as that will affect the reaction rates of the FeCl3 + Cl case.