Water Purification

Methods of Purification

Deionization

The removal of ions and minerals by synthetic ion exchange resins. Cation resins remove positively charged ions; anion resins remove negatively charged ions.

Adsorption

Activated carbon bonds with the chlorine and organic materials in feedwater to immobilize and remove these impurities.

Filtration

Use as a pretreatment or a stand-alone treatment. Water passes through a filter of specified porosity at normal line pressures. The filter retains most particulates, with water passing through.

Ultrafiltration

Use for removing pyrogens and bacteria. Under pressure, water is forced through a membrane with a pore size smaller than 0.005 µm. Particulates are retained, with only pure water passing through.

Reverse Osmosis

Use primarily as a pretreatment. Equal amounts of pure water and saline solution are separated in a U-tube by a semipermeable membrane. When external pressure is applied to the saline side, the semipermeable membrane allows water to pass through while salts are concentrated and flushed down a drain.

Distillation

The process in which water is heated to a gaseous state and recondensed in a separate vessel.

Ultraviolet (UV) Oxidation

UV light (at <280 nm) passes through the water destroying bacteria, viruses, and trace organics.

Methods of Purification Table

Method	Dissolved ionized solids	Dissolved organics	Dissolved ionized gases	Particulates	Bacteria	Pyrogens
Deionization	Excellent	Poor	Excellent	Poor	Poor	Poor
Adsorption	Poor	Excellent	Poor	Poor	Poor	Poor
Filtration	Poor	Poor	Poor	Excellent	Excellent	Poor
Ultrafiltration	Poor	Good	Poor	Excellent	Excellent	Excellent
Reverse osmosis	Good	Good	Poor	Excellent	Excellent	Excellent
Distillation	Excellent /Good	Good	Poor	Excellent	Excellent	Excellent
UV oxidation	Poor	Good	Poor	Poor	Good	Poor

ASTM Water Grade Standards

	Resistivity (MΩ-cm, min)	Conductivity (µS/cm, max)	Organic carbon (µg/L, max)	Silica (µg/L, max)	Chlorides (µg/L, max)	Sodium (µg/L, max)
Type I	18.0	0.056	100	3	1	1
Type II	1.0	1.0	50	3	5	5
Type III	4.0	0.25	200	500	10	10
Type IV	0.2	5.0	No limit	No limit	50	50