Buying guide
Laboratory Water Purification: Type I, II and III Water and How to Choose a System
Short answer
Match the water to the work. Ultrapure Type I water (18.2 MΩ·cm at 25 °C) is for HPLC, trace-metal analysis, cell culture and molecular biology. Type II water is for reagents, buffers, microbiology media and analyzer feeds. Type III (reverse osmosis) water is for rinsing glassware and feeding autoclaves and Type I systems. Size the system by daily volume and by the quality of your feed water.
Which water for which work
| Grade | Typical quality | Used for |
|---|---|---|
| Type I (ultrapure) | 18.2 MΩ·cm at 25 °C, very low TOC | HPLC and LC-MS, ICP and AAS, cell culture, PCR and molecular biology |
| Type II (pure) | Above 1 MΩ·cm | Reagents and buffers, microbiology media, clinical analyzers, pH meters |
| Type III (RO) | Reverse osmosis grade | Rinsing glassware, feeding autoclaves, dishwashers and Type I polishers |
ASTM D1193 and ISO 3696 define these grades. ISO 3696 sets maximum conductivity at 25 °C of 0.01 mS/m for grade 1, 0.1 mS/m for grade 2 and 0.5 mS/m for grade 3.
The technologies inside a system
- Reverse osmosis (RO) removes most dissolved salts, particles and organics; it is the first stage of most systems.
- Deionization and electrodeionization (EDI) remove the remaining ions to reach Type II; EDI regenerates without chemicals.
- Polishing cartridges bring water to 18.2 MΩ·cm Type I.
- UV lamps (185/254 nm) reduce organic carbon and bacteria.
- Ultrafiltration removes endotoxins, RNases and DNases for cell and molecular work.
- A 0.2 µm final filter at the dispenser holds back particles and bacteria.
Sizing the system
- Add up the litres per day of each grade, and the peak volume in one draw.
- Test your feed water: conductivity or TDS, hardness and chlorine. Poor feed water shortens cartridge life, so it changes which pretreatment you need.
- Decide whether one system should produce two grades from the same feed, which saves space and cost.
- Check the storage tank size against your peak demand.
Running costs
The purchase price is only part of the cost. Ask for the replacement interval and price of pretreatment cartridges, RO membranes, polishing cartridges, UV lamps and final filters, and how the system tells you when each is due. Monitor resistivity and TOC at the point of use, not only at the tank.
Checklist before you request a quotation
- Water grades needed and litres per day for each.
- Feed water test results.
- Critical applications: HPLC, ICP, cell culture, PCR.
- Space: bench, under-bench or wall mounting.
- Consumables, their lifetime and local availability.
- Installation, validation and service in Egypt.