Purified water is not a natural substance
This topic must be openned with the notion that purified water does not naturally occur in nature. We are talking about water, pure H20, which is actually not stable in it's pure form.  The unnatural form of purified water will try to balance itself.  It's first opportunity will be to pull carbon dioxide from the air.

By it's strick definition, purified water has had all of it's minerals stripped alway by either a process of distillation or reverse osmosis.  It is true that for some bad tap water sources, a reverse osmosis system may be necessary.  But the problem here lies with the problems for your health that purified water pose.

Purified water should not be consumed for several reasons.

• It will acidify your body
• It will leach minerals from your body
• Large molecule clusters won't hydrate well 

The idea of fasting using purified water can be dangerous.  Even though a fasting may be only for a short time, you have rapid loss of electorlytes, such as sodium, potassium and cloride.  These deficiencies can cause big problems like heart beat irregularities and high blood pressure.

Ionization of purified water will improve the body hydration capability of the water, but this is not worth it.  Vital body function minerals will be leached from the body.  Ideally, to ionize water propery, you need minerals in the water, anyway.

There is actually some controversy over the value (or detriment) to including purified water in your diet.  I, for one, don't like the idea of putting something in my body that doesn't occure in nature.  If the FDA is looking for something on the market shelf to call a drug, they should pick purified water.  But, instead, somebody got them to classify "purified water" as "drinking water". 

For situations where you think you may have tap water in need of extreme filtration, have a look at an arsenic filter by Multipure.  I am currently using a Multipure carbon filter inline with my Enagic LeveLuk SD 501 water ionizer.  With this extra filtration, I know that my water is clean.  And with the filter inline before the water ionizer, I feel I'm giving this machine a break.