Thanks to all who replied to my post:

1. First of all it's nice to hear some one else's 2 cents on the subject.
2. Yes, I know that all those kinds of messages are to be taken with a grain of salt (or some even a bag of salt :-)). It is not even safe to breathe anymore...
3. the word "poison" might have been unapropriate. Since english is not my "native" language I had trouble finding a better word (no dictionary at hand) and figured that you guys would get the point (more or less).
4. What I wanted to communicate: maybe you're better off (safer) using and rotating the water into your daily use than storing a quantity of water only for long-term-emergency-use and stretching the "usefull life" tot the limit of it before replacing it with a new supply. I have no experience in the long term storage of water. I just stock up a nice (larger) quantity of bottled (glass & plastic bottles) water for daily use with a "first in - first out" order of use.
If you really want to stock up large quantities of tap water, isn't it possible to rotate it (depending on the number of containers and quantity) e.g. having 6 batches of water of which one batch is used & replaced every month. This way you total stock is renewed every six months. If you'r stocking up more than needed for cooking and drinking, the replaced water could maybe be used for washing/flushing the toilet:...?
5. DHMO => I had never heard about it. Looks nasty.