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Your best bet would be RO/DI, spring water has additives in it. As a matter of fact, "spring water" is not FCC regulated and you are probably getting more tap water than true spring water....
Agree with the others... "spring water" is a marketing term for bottled tap water, more or less. It might go through a carbon block, but it's not pure by any means. The water that comes out of my tap originally came from a "spring".