Definition

Water with cations (Ca²⁺, Mg²⁺, Na⁺) and anions (Cl⁻, SO₄²⁻, HCO₃⁻) almost entirely removed by ion-exchange resins or electrodeionisation (EDI); conductivity <1 μS/cm, purer than RO water.

Detailed Explanation

Deionised water (DI, demineralised, demin) is produced by ion-exchange resins (mixed-bed cation + anion) or electrodeionisation (EDI) modules that strip nearly all dissolved ions. Result: conductivity 0.055–1 μS/cm (RO output is typically 5–25 μS/cm). Typical uses: pharma PW/WFI, laboratory, semiconductor, battery electrolyte, boiler feed.

Why It Matters

For steam humidifiers, DI water requires a two-sided assessment: (1) FULLY INCOMPATIBLE WITH ELECTRODE UNITS — conductivity window 125–1,250 μS/cm; DI is around 1 μS/cm → no current → no operation. (2) IDEAL FOR RESISTIVE UNITS — steam generation does not depend on water conductivity; heat transfers from the heating element. Fully pure water → zero minerals → no scale. However, DI water sits at pH 5.5–6.5 (CO₂ absorption) so corrosion risk rises; remineralisation (calcite filter, adding 1–2 ppm Ca) is recommended.

Practical Example

A pharmaceutical plant in Ankara already had DI water (for the lab and analytical instruments) and wanted a steam humidifier for a 22 °C / 45% RH cleanroom. An electrode option would not work (DI conductivity <1 μS/cm). NKT supplied a Neptronic SKE4 resistive steam humidifier, which runs on DI water; the site's water-treatment contractor also raised the pH to 6.8 by remineralisation. After commissioning, 5+ years of zero scale and a ±1% RH band; pharma GMP validation passed first time.

Engineering Note

DI water systems have high OPEX: ion-exchange resins regenerate every 6–12 months (HCl/NaOH); EDI modules are replaced every 3–5 years. Typical production cost is €0.8–2.5/m³ for DI (RO €0.3–0.8/m³, mains €0.1–0.3/m³). So DI is used only when mandatory; for simple humidification, RO is usually enough. DI feed piping must be plastic (PVDF, PP) or stainless steel (316L); copper/galvanised pipe is not used.

NKT Application Link

For this application NKT – Nem Kontrol Teknolojileri supplies the Neptronic SKE4 resistive steam humidifier and the Neptronic SKS4 steam-to-steam humidifier. Unit-selection support is based on space conditions, humidification load and the feed-water analysis; technical service and spare parts are provided. Design and installation of water treatment, as well as engineering design, installation and commissioning, remain within the scope of the facility's designer, contractor and water-treatment specialist.