Also to clarify:
Pretty much all of the distilled water at grocery stores is going to be either produced by reverse osmosis or of similar quality. So even if Pepsi's Aquafina is "pure RO/carbon filtered water" and not spring water, there is nothing special about Aquafina compared to other RO distilled other than it costs the same for a 22oz bottle as the generic stuff does for a gallon.
Pretty much all labs have 16MOhm RO water coming out of the "DI" tap at the sink. If you are a student just take a jug and grab some
