Can a newborn baby use purified water, that had been opened and unrefrigerated for 4 days, to mix formula?

Need to re-purify: Best to either boil on the stove or microwave and place in the refrigirator to cool, prior to using. After 4 days, may be contaminated with bacteria.

Puzzling question: I have seen the answer listed and am puzzled. I see no benefit to refrigerating water or sterilizing it again if it was left at room temperature. As long as the source bottle is handled in a hygienic way, it can be left at room temperature and used as needed.