Reverse Osmosis - Disadvantages

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.

Large-scale industrial/municipal systems have a production efficiency typically 75% to 80%, or as high as 90%, because they can generate the high pressure needed for more efficient reverse osmosis 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 total dissolved solids (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. A number of peer-reviewed studies have looked at the long term health effects of drinking demineralized water. 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, which adds sodium chloride (salt) and potassium chloride (salt) to its water for "taste," according to the company.