A Guide to Types of Water Used in Laboratories Part 2- ASTM Standard Types and Applications

A Guide to Types of Water Used in Laboratories Part 2 – ASTM Standard Types and Applications

In the second part of our lab water purification systems blog series, we delve deeper into the ASTM International standard classifications for water and how these classifications find their relevance within laboratory environments, examine the methods and criteria employed for water purification, and discuss the distinct purity requirements associated with each water type.

Type I - Ultrapure water

Ultrapure water is the highest grade of water purity achievable in laboratories, virtually free from impurities. It undergoes additional purification steps beyond deionisation or distillation to achieve ultralow levels of contamination. 


Ultrapure water is essential for critical laboratory procedures, including molecular biology experiments, atomic absorption spectroscopy, mass spectrometry, and high-performance liquid chromatography (HPLC).

Type I - Ultrapure water - applications

Purification method

The process of producing ultrapure water starts with pre-treatment, usually through an activated carbon adsorption filter followed by reverse osmosis water filter (RO).

Subsequently, a deionising water system using either ion exchange (IX) or electrodionisation (EDI) is employed in addition to ultraviolet (UV) water sterilisation and total organic carbon (TOC) reduction using a combination of 254nm & 185nm wavelengths. A final ultra-filter is used to capture any endotoxins. Ultrapure water is created through varying iterations of this procedure, and the specific quality criteria for the end product vary based on what it will be used for.

Resistivity, conductivity and organic compounds

Ultrapure water has the highest resistivity, at 18.2 MΩ·cm, and extremely low conductivity, usually below 0.055 µS/cm. Type I water should also have less than 50ppb in TOC.

Type II water – Purified Water

Type II water is known as purified water. It’s not ‘ultrapure’ but is pure enough for some specialised use as well as general lab applications. It’s also a feed to create Type I water. 


Within a laboratory setting, Type II water can be used for general practices, such as buffer and reagent preparations, sample dilution, microbiological analysis, PH-solution preparation, and electrochemistry. It also provides a good feed for washing machines and SST autoclaves. 

Type II water – Purified Water - application

Purification method

The processes involved in obtaining Type II water are particulate filtering, activated carbon, reverse osmosis, desalination (ion exchange or electrodeionisation), ultraviolet and microfiltration.

Resistivity, conductivity and organic compounds

The resistivity requirements for Type II water should be greater than 1 MΩ-cm and conductivity less than 1 µS/cm. The total organic compounds are typically required to be less than 50 ppb.

Type III water

Type III water has the lowest levels of purity and is suitable for general purpose applications that do not demand a high degree of water purity. 


This water is commonly used for non-critical tasks like cleaning lab equipment, rinsing glassware, heating baths, or basic solutions preparation. It can also be used as feed for autoclaves and in Type I water production.

Purification method

Type III water is produced through various methods such as filtration, reverse osmosis, or distillation and ion exchange, depending on the desired level of purity.

Resistivity, conductivity and organic compounds

Type III water must have a resistivity greater than 4 MΩ-cm and the conductivity should be less than 0.25 µS/cm. Additionally, the total organic compounds are expected to be less than 200ppb.

Using the right type of water in laboratories is crucial for a variety of scientific and experimental processes. The quality and purity of water can significantly impact the accuracy, reliability and validity of experimental results. By understanding the different types of water used in laboratories, the purification methods employed, and their resistivity and conductivity properties, lab technicians and scientists can make informed decisions about the appropriate water source for specific applications.

At Purite, we have over 40 years’ experience designing and manufacturing high performance water purification solutions for laboratory applications. This includes standard and customised units, plus custom-engineered ring-main systems. Our laboratory water systems are designed to meet your precise applications to provide the highest levels of water quality, consistency and reliability, plus low operating, and maintenance costs.

Need advice on your lab water?  Get in touch with our team.

You can read part one of our A Guide to Types of Water Used in Laboratories Part 1 here:

A Guide to the Types of Water Used in Laboratories Part 1 – Quality Standards

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