Water Purification

Water Purification

Methods of Purification    Methods of Purification Table     ASTM Water Grade Standards

Methods of Purification


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


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


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.


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.


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
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 Poor Excellent Excellent Excellent
UV oxidation Poor Good Poor Poor Good Poor

ASTM Water Grade Standards
(MΩ-cm, min)
(µS/cm, max)
Organic carbon
(µg/L, max)
(µg/L, max)
(µg/L, max)
(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