Photo Flo 600 is used at a rate of 1:600 which is way way more dilute than the 200 used at 1:200. In no way is it severely toxic dilute. The concentrate s kind of like antifreeze as noted above. I also gave 2 reasons above why 600 is not commonly used. Although a local dealer sold me nearly 1 gallon of it for about $20 about 3 years ago. I do have it and do use it.
As for Di-Hydrogen Monoxide, Stone has it identified incorrectly as to chemical nature and effects on the human body. Too much of it can actually cause suffocation. I have banned it in favor of CH3-CH2-OH. I use it in reasonable amounts and it is quite safe. The purer it is, the more effective it is as the major impurity is Di-Hydrogen-Monoxide.