I know it can leach whatever metals/materials are used in the construction of the drum. If the bottom is attached by lead solder for example, you will have lead leaching into your water.
Offered by Martha.
As far as storage is concerned, glass is best but not very practical. If you are going to store in plastic bottles, use hard plastic rather than the soft "poly" bottles. Hard plastic leeches less chemicals into the water.
Offered by Michael.
Use an activated charcoal filter to get the dissolved hydrocarbons that may have come from the plastic.
Offered by Mike.
You can also do what the old sailors did with their water storage, use a torch or fire to scorch the inside of a wooden container, i.e. your own built-in carbon filter.
Offered by Steve.