Water Deionization System: DI vs RO/EDI Buyer’s Guide

A water deionization system removes dissolved ions to produce high-purity water for industry and labs. Depending on flow, chemistry and chemical-handling policy, you can choose mixed-bed DI, RO/EDI (electrodeionization), or service DI (exchange tanks). This guide clarifies the options, shows how to size and accept a system, and links to three ready configurations you can request a quote on. If you already have specs, go straight to our EDI systems.

What Is a Water Deionization System?

Deionization removes cations and anions to reach target conductivity/resistivity. Common targets range from 1–18.2 MΩ·cm depending on process (boiler, plating, cleaning, lab Type I/II/III). Three practical routes exist: mixed-bed DI (ion-exchange), RO + EDI (no acid/caustic regeneration), and service DI (exchange tanks).

DI vs RO/EDI vs Service DI — Quick Comparison

Option	Best for	Typical Quality	OPEX & Maintenance	Pros	Watch-outs
Mixed-bed DI	Intermittent use, ultra-high resistivity polishing	Up to 18.2 MΩ·cm	Resin replace/regen (acid/caustic) or outsourced	Peak purity, fast startup	Chemicals/logistics; needs good pretreatment
RO + EDI	Continuous production ≥0.5 m³/h	~5–15 MΩ·cm (higher with polishing)	Power + cartridges + dosing; no acid/caustic	Stable, automated, operator-friendly	Requires RO; control hardness/CO₂/silica
Service DI (exchange tanks)	Temporary or small points of use	Medium–high (model dependent)	Per-tank service fee	No onsite regeneration	Unit water cost higher at scale

Match Your Need to Our 3 Ready Configurations

Choose the closest configuration and we’ll tune recovery and stack count to your water analysis. All options are engineered as a water deionization system with RO pretreatment.

Config	Typical Flow	Target Resistivity	Great For	Link
Compact RODI Skid	200 LPH (≈0.2 m³/h)	5–10 MΩ·cm	Labs, pilot skids, plating tools	200 LPH Water Deionization System (RO+EDI)
Module-based RODI	~1–3 m³/h	5–15 MΩ·cm	Electroplating, precision cleaning, boiler make-up	Water Deionization System — RO+EDI Module
High-capacity Rack	~5–20 m³/h (modular stacks)	8–15 MΩ·cm	Industrial parks, central utilities, reuse polishing	High-Capacity Water Deionization System (RO+EDI)

Not sure which fits? Compare our EDI-based water deionization systems →

Quality Targets & Monitoring

• Resistivity/Conductivity: setpoint at 25 °C; alarms and auto-divert recommended.
• TOC/Bacteria (if regulated): UV/UF or final filters as required.
• Trending: stage ΔP, temperature compensation, event/alarm logs.

Use Cases & ROI

For continuous processes, a water deionization system built on RO/EDI often lowers total cost versus service DI once flow exceeds ~0.5–1 m³/h. You eliminate acid/caustic regeneration, automate quality control (temperature-compensated resistivity), and reduce operator time. Typical wins include plating and surface finishing lines, boiler make-up, precision cleaning, lab distribution loops and electronics pretreatment. When ultra-high resistivity is required at point of use, a small mixed-bed polisher can be added downstream without changing the main skid.

Sizing a Water Deionization System

デザイン・インプット

• Feed: conductivity (µS/cm), hardness (as CaCO₃), silica, alkalinity/CO₂, temperature.
• Demand: average & peak flow (m³/h), hours/day, continuous vs batch.
• Targets: required resistivity (MΩ·cm @25 °C), TOC/bio limits if any.
• Constraints: no-acid policy, footprint, power, noise.

Typical Train

1. 50→5 µm filtration; antiscalant and pH/alkalinity management.
2. Reverse osmosis (single or double pass depending on feed/targets).
3. EDI for continuous deionization; optional polishing (UV/UF/MB).

Acceptance & Documentation (FAT/SAT)

• Permeate resistivity at temperature, flows and recovery recorded; ΔP by stage logged.
• Interlocks verified: low feed, high conductivity, auto-flush/lay-up, permissives/trips.
• Handover: GA, P&ID, IOM, spares, commissioning logs, water-test sheets.

よくあるご質問

Is RO/EDI the same as a water deionization system?

RO/EDI is one common way to build a water deionization system. Alternatives include mixed-bed DI and service DI tanks.

Can a water deionization system reach 18.2 MΩ·cm?

Yes—with proper pretreatment and polishing. Many industrial targets are 5–15 MΩ·cm.

Which option is best for intermittent use?

Mixed-bed DI or service DI is often more economical and simpler for small, intermittent points of use.

What feed limits matter most?

Hardness, alkalinity/CO₂ and silica; these determine recovery and cleaning frequency.

What should be monitored continuously?

Conductivity/resistivity at 25 °C, temperature, ΔP by stage, and events/alarms.

Can I add polishing to reach ultra-high resistivity later?
Yes. Start with RO/EDI for stable base quality, then add a small mixed-bed or cartridge polisher at the point of use to reach ultra-high resistivity when needed.

References

• ASTM D1193 — Standard Specification for Reagent Water
• USP water quality concepts for pharmaceutical use