Ditto - Although I'm sure you meant distilled water - or even better - pure water from H and O combination like from fuel cells. Which by the way - would eventually kill you - water is an almost universal solvent - you need electrolytes in the water.
Gotten off of a medical dr's web page:
Many health fanatics, however, are often surprised to hear that
drinking distilled water on a regular, daily basis is potentially dangerous.
Fasting using distilled water can be dangerous because of the rapid loss of electrolytes (sodium, potassium, chloride) and trace minerals like magnesium, deficiencies of which can cause heart beat irregularities and high blood pressure. Cooking foods in distilled water pulls the minerals out of them and lowers their nutrient value.
Distilled water is an active absorber and when it comes into contact with air, it
absorbs carbon dioxide, making it acidic. The more distilled water a person drinks, the higher the body acidity becomes.
According to the U.S. Environmental Protection Agency, "Distilled water, being essentially mineral-free, is very aggressive, in that it tends to dissolve substances with which it is in contact. Notably, carbon dioxide from the air is rapidly absorbed, making the water acidic and even more aggressive. Many metals are dissolved by distilled water."
The most toxic commercial beverages that people consume (i.e. cola beverages and other soft drinks) are made from distilled water. Studies have consistently shown that heavy consumers of soft drinks (with or without sugar) spill huge amounts of calcium, magnesium and other trace minerals into the urine.
The more mineral loss, the greater the risk for osteoporosis, osteoarthritis, hypothyroidism, coronary artery disease, high blood pressure and a long list of degenerative diseases generally associated with premature aging.
Sorry - diverged but as stated in the above post - it is the electrolytes in the water that is conductive to electricity. A very high voltage item could overcome any insulation given the amount of either.
The person who did the flashlight underwater assembly knows this. We are also dealing with sealed components. So long as the voltage is low and the distance from + to - is far enough - no immediate short would occur in regular water just from the battery. The return from the tailcap is insulated from the battery box. The electronic components are insulated from the battery box as well in the head component. However - I didn't see him fill the water from the tap - even had he - there are plenty of under sink distilled water purifiers. I think - since I don't speak Chinese - that he was demonstrating the sealed components effectiveness, for had the head components and circuitry been exposed to tap water - they would have shorted unless the water were pure.
