What Is Pure Water? A Technical Guide Into Type 1-3 Ultrapure Water Systems

what is pure water guide

What Is Pure Water?

High purity water, commonly referred to as laboratory-grade water, is water that has been purified to remove nearly all contaminants, such as dissolved minerals, organic compounds, and microbial organisms. The purity level and specification of water type are essential in various scientific and technical applications to prevent any interference with experiments or processes.

In commercial and industrial settings, high purity water is crucial for ensuring the accuracy and reliability of experimental results and manufacturing processes. It is used extensively in fields such as pharmaceuticals, biotechnology, electronics manufacturing, and chemical testing as the absence of impurities prevents unwanted reactions, which could skew results or damage sensitive equipment.

Types of Ultrapure Water Systems: Overview

Ultrapure water systems are categorized into three types based on the level of purification and the intended use:

  • Type III Standard Laboratory Water: Although it is the lowest grade among the three, Type III water is suitable for non-critical applications such as rinsing glassware, filling autoclaves, and other uses where high purity is not essential.
  • Type II High Purity Water: Used for general laboratory applications, including preparation of microorganism culture buffers and media, and analytical procedures that require water of high purity but not as rigorously controlled as Type I ultrapure water. This includes applications such as media and buffer preparation, sample dilution, and some instrumental analyses.
  • Type I Ultrapure Water: This is the highest grade of laboratory water and is used for the most critical applications for sensitive analytical methods like high-performance liquid chromatography (HPLC), gas chromatography (GC), and mass spectrometry (MS). Additionally, molecular biology applications, such as PCR, DNA sequencing, and cell culture, rely on Type I water due to its very low contamination levels.

Each type of water is critical for different laboratory tasks, ensuring that all processes are conducted under controlled and contaminant-free conditions.


Ultrapure Water Specifications: How To Measure Water Purity

testing ultrapure water specifications

Measuring the purity of water involves several crucial parameters and techniques to assess its suitability for various applications, especially in scientific and industrial settings. Here is an overview of the key qualities and specifications utilized to measure the purity of water.


Resistivity is a critical parameter for measuring water purity, particularly in high purity water systems. It indicates the ability of water to resist the flow of electric current. High resistivity values suggest fewer ions in the water, meaning higher purity. This measurement is particularly important in environments where ionic contamination can affect processes, such as in semiconductor manufacturing or analytical laboratories. Resistivity is typically measured in megaohms-cm (MΩ-cm), and ultrapure water typically has a resistivity close to 18.2 MΩ-cm at 25°C, which is the theoretical maximum.


Conductivity is the inverse of resistivity and measures the ability of water to conduct electrical current. It is directly related to the concentration of ionic contaminants in the water. Conductivity is used alongside resistivity as a standard measure of water purity, particularly useful for ongoing monitoring in industrial processes. It is usually measured in microsiemens per centimeter (µS/cm), with lower values indicating higher purity. For Type I ultrapure water, conductivity is typically less than 0.056 µS/cm at 25°C.

Total Organic Carbon (TOC)

TOC is a measure of the amount of carbon found in organic compounds in water. In high purity water systems, TOC is used as a measure of organic contamination, which can affect both the chemical and biological reactions in laboratory and industrial processes. Lower TOC levels are indicative of higher water purity, crucial for industries where organic contamination can compromise product quality or research outcomes.

pH and Oxygen content

While not directly related to water purity, the pH and oxygen water levels are used as indicators for water contamination by providing key information on the water chemistry. Significant deviations from neutral pH can indicate chemical contamination, which may affect experimental outcomes or product quality. On the other hand, abnormal oxygen levels might suggest microbial activity or the presence of certain chemical contaminants, which can be critical in processes where oxidation or reduction reactions are sensitive to oxygen levels.

Inductively Coupled Plasma Mass Spectrometry (ICP-MS)

The ICP-MS is a sophisticated ultrapure water specifications indicator that is used to detect and quantify trace elements and heavy metals in water. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) offers high sensitivity and the ability to detect trace elements at parts per trillion levels. It is a key water quality index in environmental monitoring, toxicology studies, and materials science.

Atomic Absorption Spectroscopy (AAS)

Another advanced spectroscopic method is the Atomic Absorption Spectroscopy or AAS. This measures the absorption of light to assess the presence of metal ions in water. It is widely used in clinical analysis, pharmaceuticals, and chemical manufacturing.

Microbial Analysis

High purity water must have minimal microbial presence. Techniques such as membrane filtration followed by culturing on selective media or direct enumeration using microscopic techniques are used to assess the microbial content. Endotoxin testing is another parameter where endotoxins (components of the outer membrane of gram-negative bacteria) are detected and quantified for control.

Particulate Measurement

The presence of particulate matter can be a significant concern in high purity water, especially where even microscopic particles can impair processes such as semiconductor fabrication or injectable pharmaceutical production. Measurements are typically performed using light scattering methods or microscopic analysis to determine the size and quantity of particles.


Types of Ultra Pure Water: Key Characteristics

types of ultrapure water system

Determining the purity level of water is essential in laboratory and industrial settings. The ultrapure water specifications provide a clear distinction between types and their suitability for certain applications. Here is a deeper description of the different types of water systems for industrial use.

Type III: Lowest Purity

Conductivity and Resistivity Ranges

According to the American Society for Testing and Materials (ASTM), Type III water has a conductivity that should be less than 0.25 microsiemens per centimeter (µS/cm) and a resistivity of at least 4.0 megaohms-cm (MΩ-cm). These values indicate that while Type III water is the least pure of the laboratory-grade waters, it still maintains a significant level of purity suitable for various general laboratory needs. Max TOC of 200 µg/L; Max Silica of 500 µg/L;


Type III water is commonly used in basic laboratory applications that do not require the highest degree of purity. This includes uses such as preparing solutions for routine testing and analyses, cleaning glassware and other laboratory instruments, and as feed water for clinical analyzers. Its relatively lower cost and purity level make it suitable for these non-critical applications where high levels of contaminants are not likely to interfere with the outcomes of the procedures.

Purification Techniques

The primary purification method used for producing Type III water is Reverse Osmosis (RO). RO involves passing water through a semipermeable membrane that blocks contaminants but allows water molecules to pass through. This method effectively reduces dissolved inorganics and some types of organic compounds and microbes. Due to its reliance on RO technology, Type III water is often referred to as RO water. While RO significantly improves the purity of water, it does not remove all contaminants to the extent required for Type I or Type II water, thus categorizing it as the lowest tier of ultrapure water in laboratory settings.

  • Our Pick: The LaboStar® Pro TWF systems from Evoqua offer an effective solution for converting tap water to ultrapure water. This system delivers both Type I and Type III water, ideal for a range of laboratory applications. Type I water, dispensed directly, achieves a resistivity of 18.2 MΩ-cm and a TOC between 1-10 ppb, suitable for critical scientific work. The system incorporates a pre-filtration unit, a reverse osmosis membrane, and a polishing module to ensure high purity. Additionally, it features a conductivity sensor for real-time purity monitoring and options for different sterile filters to remove bacteria and endotoxins. This system is particularly well-suited for environments requiring reliable production of analytical-grade water on a moderate scale.

Type II: Intermediate Purity

Conductivity and Resistivity Ranges

Type II water typically exhibits a conductivity level of about 0.1 to 1.0 microsiemens per centimeter (µS/cm) and a resistivity between 1 to 10 megaohms-cm (MΩ-cm), as specified by the American Society for Testing and Materials (ASTM). These values reflect a higher degree of purity than Type III water, positioning Type II as suitable for more sensitive applications within laboratory settings.


Type II water is commonly utilized for analytical purposes where higher purity is required but where the ultimate purity of Type I is not necessary. Common applications include the preparation of reagents, buffers, and media for microbiology and cell culture operations; as feed water for Type I systems; and for general lab equipment such as autoclaves and glassware washers. It is also used in the qualitative analytical procedures where Type I water is not a strict requirement.

Purification Techniques

The purification process for Type II water typically includes a combination of Reverse Osmosis (RO) and deionization (DI). RO reduces a substantial portion of inorganic ions and larger organic molecules, while DI further removes ionized species through ion exchange processes. This combination effectively increases the purity level of the water, making it appropriate for a broader range of sensitive applications compared to Type III water. The use of these combined technologies ensures that Type II water meets the intermediate purity requirements necessary for many standard laboratory operations. Max TOC of 50 µg/L; Max Silica of 3 µg/L;

  • Our Pick: The Thermo Scientific™ Barnstead™ TII Type 2 Water System is designed to produce Type 2 pure water, surpassing ASTM and CLSI-CLRW standards, making it ideal for applications such as media preparation, buffer preparations, glassware washing, and as feed water for Type 1 ultrapure water systems. This system employs a multi-step purification process that includes pretreatment, reverse osmosis, deionization, UV oxidation, and filtration to ensure the removal of contaminants and the provision of high-quality water. Its sophisticated control system monitors water quality at every stage, providing real-time data to ensure consistency and reliability in water purity.

Type I: Ultrapure Water

Conductivity and Resistivity Ranges

Type I water is the highest grade of laboratory-grade water, characterized by its exceptionally low conductivity, typically less than 0.056 microsiemens per centimeter (µS/cm) at 25°C, and its high resistivity, close to 18.2 megaohms-cm (MΩ-cm). These measurements, as per the standards set by the American Society for Testing and Materials (ASTM), reflect the ultra-high purity of Type I water, making it ideal for the most demanding laboratory applications.


Type I ultrapure water is essential for applications where the slightest impurities could cause significant errors or damage. This includes critical scientific and medical research tasks such as high-performance liquid chromatography (HPLC), gas chromatography (GC), molecular biology (e.g., PCR, DNA sequencing), and cell culture. It is also used in the preparation of standards and reagents for trace element analysis and other applications where the highest accuracy and reliability are crucial.

Purification Techniques

To achieve this high level of purity, Type I water undergoes multiple stages of purification. Initially, the water is treated through both Reverse Osmosis (RO) and deionization (DI) to remove a significant portion of ionic and organic contaminants. This is followed by additional purification steps such as ultrafiltration, which removes particulates and microorganisms, and ultraviolet (UV) light treatment, which effectively reduces the levels of organic compounds through photolysis and controls microbial contamination through germicidal irradiation. Often, a final step of polishing using specialized DI cartridges is employed to ensure the removal of any remaining ionized impurities, achieving the highest purity levels required for Type I water. Max TOC of 50 µg/L; Max Silica of 3 µg/L;

  • Our Pick: The Thermo Scientific™ Barnstead™ GenPure™ Pro Water Purification System is designed to produce Type 1 ultrapure water, ideal for various scientific and research applications. This system integrates advanced technologies including UV photo-oxidation, ultrafiltration, and TOC (Total Organic Carbon) monitoring to ensure exceptional water purity. Its compact and flexible design allows for easy installation on a laboratory bench or wall, enhancing accessibility and convenience. The system also features real-time monitoring of water purity and smart consumables, which help maintain and extend the system's performance and reliability.



What is considered high purity water?

High purity water is water that has been treated to remove almost all contaminants including ions, organics, and microbes. It is typically used in laboratories and industrial processes where the presence of impurities can interfere with scientific experiments and manufacturing.

What is the highest water purity?

The highest water purity is Type I ultrapure water, which has a resistivity of 18.2 megaohms-cm and virtually no organic or inorganic contaminants. It is used for the most sensitive and critical laboratory and industrial applications.

Can we drink ultrapure water?

No, it is not recommended to drink ultrapure water regularly as it lacks minerals and salts essential for human health and can cause mineral imbalances in the body if consumed in large amounts.

Is ultrapure water the same as distilled?

No, ultrapure water is not the same as distilled water. Ultrapure water undergoes more rigorous purification processes, including reverse osmosis, deionization, and often ultraviolet treatment, achieving higher purity levels compared to distilled water, which primarily removes impurities through evaporation and condensation.

Does ultra pure water dissolve metal?

Yes, ultrapure water can dissolve metals. Due to its high purity, it is highly aggressive in leaching metals from contact surfaces, especially under certain conditions, because it seeks to equilibrate by absorbing carbon dioxide and ions from its environment.

What are the specs of ultra pure water?

The specifications of ultrapure water typically include a resistivity of 18.2 megaohms-cm, conductivity less than 0.056 microsiemens per centimeter at 25°C, very low levels of Total Organic Carbon (TOC), and negligible amounts of dissolved solids. It also undergoes testing for microbial contamination to ensure it meets stringent purity standards.

The material provided in this article is for general information purposes only. It is not intended to replace professional/legal advice or substitute government regulations, industry standards, or other requirements specific to any business/activity. While we made sure to provide accurate and reliable information, we make no representation that the details or sources are up-to-date, complete or remain available. Readers should consult with an industrial safety expert, qualified professional, or attorney for any specific concerns and questions.


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Author: Lazar Nesovic

Lazar Nesovic, a TRADESAFE representative with a B.S. and Ph.D. in Chemical Engineering from Texas Tech University, excels in process engineering and skin immunotherapy research. His work, including a significant publication on allergen immunotherapy and a provisional patent, has secured over $5 million in research funding. Alongside his academic and professional achievements, Lazar has demonstrated leadership in various roles and is dedicated to community service, including volunteering for the National Alliance on Mental Illness. His expertise greatly enhances TRADESAFE's commitment to safety and development.