Here are the claims...
PiMag water also offers more. Decades ago, scientists discovered that the water in a remote area of Japan produced amazing results on the surrounding plants. They named it pi water. Nikken has succeeded in replicating the environment that created pi water in nature, and these discoveries are incorporated in PiMag products. You will taste and feel the difference!
And here's the detractors:
Pi Water is a name given to various commercial water products that are purported to be enhanced in mysterious ways in order to benefit the body and living things in general. "Pi Water" is registered as a trademark with the USPTO, assigned to Pi-Tech America Inc of Chicago which seems to have a very low profile. Both Pi Water and PiMag™ Water (described further below) are widely available through multi-level marketing schemes.
The concept of Pi Water apparently originated in Japan, a country that seems to be obsessed with water-quackery. Credit has been given in various places to different individuals—Kushi, Masuda, Tatanabe, Yamashita, and even the notorious Dr. Jhon. One story about the "discovery" of Pi Water says
It was originally thought a hormone was responsible for causing plants to bud. Dr.Yamashita was conducting research, attempting to isolate this hormone, when he discovered that what was causing the flower to bud was not a hormone at all but a very minute amount of ferric ferrous salt. In 1964, Dr. Yamashita, an agricultural scholar furthered his research and found that this substance had other highly beneficial qualities.
(This is erroneous nonsense, of course; no reports of this in the scientific literature are cited.)