Demineralized water is water from which almost all dissolved salts have been removed. In practice it usually means water with a conductivity below about 10 µS/cm, and much lower for power plants, electronics and pharmaceuticals. Its quality directly affects product quality and equipment life, so the treatment line must be chosen carefully.
Where demineralized water is used
- Boiler feed water in power plants and factories
- Pharmaceutical production and laboratories
- Electroplating and surface finishing
- Electronics and semiconductor rinsing
- Hospitals, batteries and cosmetics
Main treatment methods
Ion exchange. Cation resin replaces calcium, magnesium and sodium with hydrogen ions, and anion resin replaces chloride, sulfate and silica with hydroxide ions. A two-bed system (cation + anion) is simple and reliable but needs acid and caustic for regeneration.
Reverse osmosis (RO). RO membranes remove 95–99% of dissolved salts without chemicals for regeneration. RO is now the usual first stage, reducing the load on downstream polishing.
EDI (electrodeionization). EDI modules use resin and an electric field to remove the remaining ions after RO. The resin is regenerated continuously by electricity, so no acid or caustic is needed.
Mixed bed polishing. A column with mixed cation and anion resin gives very high purity and is used as the final step when conductivity must be extremely low.
Distillation is still used for small volumes in laboratories and pharmaceuticals, but its energy use makes it costly for industrial flows.
How to choose the right line
The choice depends on the feed water analysis, the required conductivity and silica, the flow rate and whether the plant can handle regeneration chemicals. A common modern line is pre-treatment (sand, carbon, 5 µm cartridge), then RO, then EDI or a mixed bed. TIPA engineers can review your water analysis and propose a line with the lowest total cost over the life of the system.
