Reverse osmosis (RO) is a popular method of water filtration. Water is pushed through a semi-permeable membrane, which eliminates germs, pollutants, and, sadly, mineral ions. RO water is thus pure but demineralized water deficient in critical minerals such as sodium, potassium, calcium, magnesium, and other dissolved solids.

Traditionally, the use of RO water was limited to laboratories and industry; however, as water pollution has increased, the application of RO water purification has spread to the average man, who now uses RO water filters to purify water for daily use.