Usually a non-RO water purifier company will tell you that their system can filter harmful contaminants and retain good minerals in the water. This is only half truth.
Chemicals are generally categorized into organic chemical or inorganic chemical. To know which chemical is organic or inorganic, you can Google the name of the chemical and if the chemical structure has a carbon atom or 'C' in it, then it's an organic chemical.
Good minerals are in the form of inorganic chemical. If a water purifier system allows good minerals to bypass, logically it also allows other inorganic contaminants to bypass. Most of the system in the market I've seen which allow good minerals to bypass are activated carbon filter. Organic contaminants contain carbon molecules which can bond to the activated carbon filter. A well designed activated carbon filter can filter organic chemicals and some inorganic chemical such as chlorine, lead and mercury. The disadvantage of activated carbon filter is it's not effective in removing most inorganic contaminants such as arsenic, nitrate, or heavy metals like chromium and cadmium. RO membrane can filter these inorganic contaminants. Most RO system also have pre- and post-activated carbon filter to filter organic contaminants. So a well designed RO system can filter both organic and inorganic contaminants.
There is no filter in the market which can differentiate between good minerals and bad minerals. This is a marketing gimmick. If the filter can retain good minerals in the water, chances are it also retains other inorganic chemicals in the water.
I do not deny the fact that some minerals in the water are essential to our health such as calcium and magnesium. Individuals who does not maintain a healthy diet can benefit from the calcium and magnesium content in the water to prevent certain illnesses. For those who drink RO water, the lack of minerals in the water can be supplemented from food intake. http://www.iwawaterwiki.org/xwiki/bin/view...les/RO_Minerals
Between a choice of drinking filtered water containing good minerals plus inorganic contaminants, or RO water which doesn't contain organic and inorganic contaminants while lacking good minerals, I personally choose RO water and supplement the minerals from food and nutrient supplement intake. A glass of milk contains more calcium than a glass of water.
The are some precautions on drinking RO water though:
1) Don't fill RO water in plastic bottle because of leaching effect. It's best to fill RO water in glass or stainless steel bottle.
2) It's not recommended to drink RO water immediately after exercise. Better drink 100plus to replenish the salt lost through sweats.
3) Maintain a healthy diet or take nutrient supplements if you're to drink RO water.