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Disadvantages
Household reverse osmosis units use a lot of water because they have low back pressure. As a result, they recover only 5 to 15 percent of the water entering the system. The remainder is discharged as waste water. Because waste water carries with it the rejected contaminants, methods to recover this water are not practical for household systems. Wastewater is typically connected to the house drains and will add to the load on the household septic system. An RO unit delivering 5 gallons of treated water per day may discharge anywhere between 20 and 90 gallons of waste water per day.[10] For household use, however, and based on consumption of half a gallon per day, this may amount to less than a toilet-flush per day.
Large-scale industrial/municipal systems have a production efficiency typically 75% - 80%, or as high as 90%, because they can generate the high pressure needed for more efficient RO filtration. On the other hand, as efficiency of waste-water rates increases in commercial operations effective removal rates tend to become reduced, as evidenced by TDS counts.
Due to its fine membrane construction, reverse osmosis not only removes harmful contaminants that may be present in the water, it also strips many of the good, healthy minerals from the water as well, thereby making the water quite acidic.[citation needed] Reverse Osmosis water is, in fact, so chemically unstable and acidic that in many countries national plumbing codes restrict water that has been filtered via reverse osmosis from being reintroduced into copper pipes due to its corrosiveness on the copper. This also has implications for reverse osmosis filtration systems that use steel storage tanks, as the acidity of the water can lead to the steel rusting over time and contaminating the post-filter water.
A number of Peer-reviewed studies have looked at the long term health effects of drinking demineralized water[11]. However, demineralized water, can be remineralized, and this process has been done in instances when processing demineralized water for consumption. An example of this process is Dasani.
http://en.wikipedia.org/wiki/Reverse_osmosis#Disadvantages
Health effects of drinking purified water
Distillation removes all minerals from water, and the membrane methods of reverse osmosis and nanofiltration remove most, or virtually all, minerals. This results in demineralized water which has not been proven to be healthier than drinking water.[citation needed] The World Health Organization investigated the health effects of demineralized water in 1980, and its experiments in humans found that demineralized water increased diuresis and the elimination of electrolytes, with decreased serum potassium concentration. Magnesium, calcium and other nutrients in water can help to protect against nutritional deficiency. Demineralized water may also increase the risk from toxic metals because it more readily absorbs them, and because the presence of calcium and magnesium in water can prevent absorption of lead and cadmium. Recommendations for magnesium have been put at a minimum of 10 mg/L with 2030 mg/L optimum; for calcium a 20 mg/L minimum and a 4080 mg/L optimum, and a total water hardness (adding magnesium and calcium) of 24 mmol/L. At water hardness above 5 mmol/L, higher incidence of gallstones, kidney stones, urinary stones, arthrosis, and arthropathies have been observed. For fluoride the concentration recommended for dental health is 0.51.0 mg/L, with a maximum guideline value of 1.5 mg/L to avoid dental fluorosis.[16]
Water filtration devices are becoming increasingly common in households. Most of these devices do not distill water, though there continues to be an increase in consumer-oriented water distillers and reverse osmosis machines being sold and used. Municipal water supplies often add or have trace impurities at levels which are regulated to be safe for consumption. Much of these additional impurities, such as volatile organic compounds, fluoride, and an estimated 75,000+ other chemical compounds[17][18][19] are not removed through conventional filtration; however, distillation and reverse osmosis eliminate nearly all of these impurities.
The drinking of purified water as a replacement of drinking water has been both advocated and discouraged for health reasons. Purified water lacks minerals and ions such as calcium that play key roles in biological functions such as in nervous system homeostasis, and are normally found in potable water. The lack of naturally-occurring minerals in distilled water has raised some concerns. The Journal of General Internal Medicine[20] published a study on the mineral contents of different waters available in the US. The study found that "drinking water sources available to North Americans may contain high levels of calcium, magnesium, and sodium and may provide clinically important portions of the recommended dietary intake of these minerals". It encouraged people to "check the mineral content of their drinking water, whether tap or bottled, and choose water most appropriate for their needs". Since distilled water is devoid of minerals, supplemental mineral intake through diet is needed to maintain proper health.
The consumption of "hard" water (water with minerals) is associated with beneficial cardiovascular effects. As noted in the American Journal of Epidemiology, consumption of hard drinking water is negatively correlated with atherosclerotic heart disease.[21]
Where a public water supply contains significant fluoride, naturally or added by fluoridation, people who prefer to limit fluoride intake can install filters appropriate to reduce fluoride content.
http://en.wikipedia.org/wiki/Purified_water#Health_effects_of_drinking_purified_water
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Sgt.Oat  
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27 ก.ค. 55 09:15:46
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น้ำดื่มระบบ Reversr osmosis(RO) เป็นอันตรายจจริงหรือไม่ครับ
