Selecting the right high purity water system is critical for engineers, facility managers, and engineering firms designing laboratory, healthcare, and industrial applications. Water softening, reverse osmosis (RO), and deionization (DI) are three of the most common treatment methods. Understanding when to use one, two, or all three can significantly impact system performance, operational costs, and efficiency.
At Atlas High Purity Water, we help customers and engineering teams make the right choice using a straightforward, application-driven approach built around three key factors.
Common Applications, Purity Ranges, and Filtration Considerations
Water resistivity or conductivity does not significantly change through standard filtration alone. To meaningfully alter resistivity, total dissolved solids (TDS) must be removed via RO or DI. It’s also important to note that setting and maintaining a precise resistivity setpoint is difficult—controlling exact levels of dissolved solids is nearly impossible.
Typical industry requirements include:
| Application | Typical Purity Requirements |
|---|---|
| Clinical Labs | Type I water (>10 MΩ·cm resistivity, <0.1 µS/cm conductivity) |
| Central Sterile Processing | AAMI ST108 Critical Water (<1 µS/cm conductivity, >1 MΩ·cm resistivity) |
| Pharmaceutical Systems | USP Purified Water (<1.3 µS/cm at 25°C, >0.77 MΩ·cm resistivity) |
| Humidification Systems | 10–100 µS/cm conductivity (10K–100K ohm resistivity), varies by equipment design |
| Autoclaves | Carbon steel units typically use softened water; stainless steel models may require DI water (1–5 µS/cm conductivity or as pure as 18.2 MΩ·cm) |
| Dishwashers | Typically 50–100 µS/cm conductivity (10K–20K ohm resistivity); some require DI for optimal cleaning |
Water Softening: Protecting Equipment from Scale
Water softening removes calcium and magnesium ions, preventing hard water scale in boilers, humidifiers, and RO systems. Softened water typically ranges from 100–500 µS/cm conductivity (2K–10K ohm resistivity), depending on the incoming tap water.
Key benefits:
- Prevents scale formation and mineral fouling.
- Protects heat exchangers, humidifiers, steam generators, and RO membranes.
- Essential as pretreatment for most RO systems.
Reverse Osmosis (RO): Efficient Reduction of Dissolved Solids
RO uses semi-permeable membranes to remove up to 99% of dissolved solids, organics, and particulates. It is commonly used when moderate to high purity water is required, either as a standalone treatment or as a pretreatment step before DI.
Typical RO water quality: 5–50 µS/cm conductivity (20K–200K ohm resistivity)
Key benefits:
- Reduces TDS before DI, significantly extending resin life.
- Ideal for humidifiers, autoclaves, dishwashers, and general lab use.
- Lower service requirements compared to DI-only systems.
Deionization (DI): Achieving Ultrapure Water Standards
Deionization removes nearly all ionic contaminants, delivering the highest purity water for mission-critical applications.
Typical DI water quality: 0.055–1.0 µS/cm conductivity (1 MΩ–18.2 MΩ resistivity)
Key benefits:
- Provides ultrapure water for biotech, semiconductor, and pharma.
- Compact, adaptable, and serviceable across a wide range of industries.
- Used in central sterile processing, R&D labs, and precision manufacturing.
When RO and DI Are Used Together
Many high purity water systems incorporate both RO and DI to balance performance, efficiency, and cost. RO removes most contaminants upfront, reducing the workload on DI resin and extending service intervals.
Use RO + DI together when:
- Continuous high-purity water is needed with minimal downtime.
- Operating costs must be optimized by reducing DI resin replacement frequency.
- Regulatory compliance or process consistency is required (e.g., healthcare, biotech, life sciences).
In multi-use facilities, it’s often necessary to distribute both RO and DI water separately to meet different system requirements. This is achieved with dedicated skids, distribution loops, and storage tanks for each purity level.
Conclusion
Choosing between softened water, RO, and DI—or a combination—depends entirely on the unique requirements of your facility and the equipment in use. Understanding application-specific purity standards and how each treatment method performs ensures your system operates reliably and cost-effectively.
Atlas High Purity Water specializes in designing, fabricating, installing, and servicing high purity water systems tailored to your facility’s needs. Contact us today to find the right solution for your application.