From the very beginning of the first Mistborn book Vin is able to use 'Luck' on people, a power she derives from burning metals she has ingested. The question is, before she is aware of the nature of her power, and therefore before she purposefully ingests the metals she is able to use her powers.
Where does her metal come from? I'm well aware that Kelsier and Dockson speculate she is able to use the trace minerals in the water, but I would like to see some evidence to the case. The clue here is the word 'trace', it seems like there couldn't be enough in the water. Do average mineral levels in a mining town support the fact she has access to enough of the metals or is her use of trace minerals supported elsewhere?