There is no standardized definition of purified water. In consumer products the term Purified Water is used as a marketing gimmick to sell the consumer on the concept of a more healthy, safer drinking product. In industry there are many different types of purified water with specification designed for particular applications. Industrial grades of purified water include different grades of Electronic Grade, Food Grade, United States Pharmacopoeia, and even different analytic grades for things like Dialysis (AAMI) and Laboratory (ASTM et. al).
There are many different technologies to “filter” or “purify” water, but really there is no universal convention to describe what purified water is. One may call water that has sediment removed, purified. Another may consider Reverse Osmosis water to be purified. Because of the extreme marketing value of any entity called “purified water” many people use the term as a way of insinuating that water treated by the particular technology they are selling is “purified” and somehow better than all other water.
The only crucial issue in determining what the term purified water really means is to examine the water analysis. By doing that, one eliminates having to consider whether the associated technologies used to produce that water are effective or not, and instead focus on whether the water quality itself is good enough for one’s needs.