Wow, lots of good water questions on the blog. Water is super important for good health. Please see my other posts about water quality in the wilderness and drinking too much water.
Yes, it is true that tap water and even bottled water can have higher than desired levels of heavy metals and other contaminants. It varies greatly from place to place, some cities have very clean water and others not so good. Many people believe drinking bottled water will ensure they have clean water - this is false. Most bottled water is actually just tap water bottled up! And it is subject to the same standards as tap water - it is not necessarily cleaner. Plus, bottled water costs a lot, is shipped and trucked around the world, and creates all kinds of extra waste and bottles that wind up in the landfill. Bottled water is a big waste of money and natural resources.
To ensure clean drinking water, the best way is through use of home filtration systems. Refrigerator cartridges and other stand alone systems are the best. Faucet filters and pitcher filters do remove some contaminants, but are not as good as others. The best thing to do is to read the actual product literature - it will list which contaminants are removed by the filter, and what amounts it is guaranteed to remove. This will be a giant list of chemical names and amounts, such as parts per million (ppm) or micrograms per liter (ug/L). Especially check for heavy metals like arsenic, cadmium, lead, etc. Also, this independent website is a great source for third party information on water filtration systems. http://www.nsf.org/certified/dwtu/
There is no need to spend multi-thousands of dollars on a water system though. I have a Maytag brand water filter cartridge in my refrigerator, and it does a very good job on common contaminants. It only costs $30 every six months. Most filters use activated carbon technology (or some variation). Reverse osmosis is way overkill - that is what drug companies use to prepare water for use in drugs for injection. You don't need reverse osmosis.
As for the beneficial minerals advertised in bottled waters like FIJI, your body doesn't really need that. The chemical structure of water is H2O - that's what you need. You do need small amounts of micronutrients and vitamins to be healthy, and that is what food is for. Your body needs salt, potassium, and calcium to keep your nerves and heart running smoothly. Your body automatically regulates all of this if you drink water and have a healthy diet. Your body is an awesome, efficient balancing machine, and tweaks its own pH, minerals, and water/salt balance all by itself. Bottled water companies are trying to make a lot of money from their water and make some pretty outrageous health claims.
I've never heard of "dead water" in terms of drinking water. Dead water is usually brackish fresh water that sits on top of salt water. However, there is no such thing as the fountain of youth (in terms of water), and magical minerals in water are no more magical than a balanced, healthy diet.