Comparing the 4 Types of Laboratory Water

The water available on the earth is used for different purposes. The water available in the natural resources has a lot of contaminants in it. It is purified for drinking purposes as per the local and national regulations with acceptable colour, odour, and taste.  This water is purified in four levels of purity as recognized by the water purification industry. Each level of purity has standard specifications by various organizations such as ASTM, ISO, CLSI, and more.

The purity and quality of the water are determined with various measurements of resistivity MΩ-cm) or conductivity (µS/cm), Total Organic Carbon (TOC) in ppb (Parts Per Billion), bacterial count(CFU/ml), and particles  0.2(µm/ml).

Here we discuss the four grades of water in the laboratories and the process that is used to get lab purified water.

Types of Laboratory Water

1. Feed Water

Feedwater is the portable water on the tap. The quality of the feed water is dependent on the source. Underground water is usually hard with more inorganic contaminants, reduced organic contaminants and is naturally filtered by a layer of rock and soil. Water from surface sources like lakes, rivers, and reservoirs are richer in organic contaminants than inorganic contaminants.

The water from the natural resources is easily identified by its colour, odour and turbidity. The factors that are measured to identify the source of the water are pH, hardness as well as bacteriological characteristics.

Major contaminants of feed water include inorganic ions, organic compounds, particles, or microorganisms. It is important to determine the contaminants present in the feedwater and pretreatment measures are undertaken to prevent damages in the subsequent purification methods.

General pretreatment methods are depth filters and activated carbon in the pretreatment stage. 

Depth filters are matted fibres. In this process, the raw water is passed through the matted fibres which are typically in the range of 1-50 μm. It is an economical way of trapping suspended impurities from the water. 

Activated carbon is also an important method to remove the chlorine ions present in water. The chlorine present in the water largely damages the Reverse Osmosis (RO) membrane. It is important to soften the water i.e., reducing the hardness of the water. The hardness of CaCO3 present in the water forms scales in the RO membrane and reduces its lifespan.

2. Primary Grade Water (Type 3)

Primary grade water is generally referred to as Type 3. This grade of lab purified water is processed with carbon filtration and RO technology, it is the most cost-effective method to remove contaminants from the water.

Reverse Osmosis (RO) process in which the pressure is applied to reverse the osmotic flow so that the water is forced through the membrane and deposits the impurities in the membrane. This RO process removes almost all types of contaminants (inorganic, organic, or bacteria) on the surface. Nearly 95% of the contaminants of the feedwater are removed by this process.

Reverse osmosis technology applies the diffusion technique by rejecting the particles with higher molecular weight. This process rejects the particles depending on several factors such as temperature, pressure, and the RO membrane. The rate of rejection of contaminants differs from the feedwater contaminants. And hence RO water cannot be specifically classified.

Reverse Osmosis is a commonly used basic water purification process for laboratory applications. This RO purified Type 3 water generally has resistivity >4 MW-cm, TOC <200 ppb, and bacteria 10cfu/ml as per ASTM standards. It is used in various laboratory applications such as glassware rinsing, autoclaves, as a  feed to the ultrapure water system for the laboratory, and many other non-critical applications.

3. General Laboratory Grade Water (Type 2)

General laboratory grade water is commonly referred to as Type 2 water. This Type 2 water is generally produced through a combination of methods like reverse osmosis and ion exchange or Electro-Deionization (EDI).

Deionization or ion exchange resins are synthetic resins that remove ionic components from the RO water. When the water is passed through the resins chemical reaction occurs that replaces the cations with hydrogen (H+) ions and anions are replaced by hydroxyl (OH-) ions. These hydrogen and hydroxyl ions are combined to form pure water removing other ionic (inorganic) contaminants.

EDI (Electro-Deionization) is commonly used in water purification systems laboratories. This process combines electrodialysis with ion exchange. In this process, an anode and cathode are placed on both sides of the ion exchange resin. DC current is applied to the electrodes; the anions present in the water are attracted to the anode and the cations present in the water are attracted to the cathode. Water is passed through the EDI cell chamber fixed with a loosely packed ion exchange resin that removes the ionic contaminants from the water effectively. 

The RO process followed by the EDI process used in the water purification system for the laboratory effectively increases the resistivity of the water by removing the inorganic components from the water. By this combined process Type 2 water is produced with resistivity > 1.0MΩ-cm, TOC< 50 ppb, and bacteria 0.1 CFU/ml as per ASTM standards. This Type 2 water is used in various general laboratory applications such as buffer, media preparation, general chemistry and spectrophotometry.

4. Ultrapure Water (Type 1 - Ultrapure water system for the laboratory)

In the water purification system for the laboratory where the Type 2 water is produced by RO and EDI, the process removes inorganic components effectively but does not remove any of the organic impurities, bacteria or pyrogens.

The water purification system for the laboratory that produces the Type 1 water is referred to as a polisher. Usually, RO pretreated water or Type 2 water is fed as input to produce Type 1 water (Ultrapure water system for the laboratory). The resistivity of this ultrapure water is 18.2 MΩ-cm at 25°C that still contains organic impurities, bacteria or nucleases.

Contaminants such as organic, bacteria, endotoxins or pyrogens are eliminated by using UV photo-oxidation technology. UV light with a wavelength of 185 nm and 254 nm is used. Generally 254 nm UV light wavelength is the germicidal wavelength that damages the DNA of the bacteria and kills them when the water passes through the UV chamber. Even though the bacteria is killed it is not removed from the water. Ultrafilter (UF) is used to remove dead bacteria and used to produce DNase/RNase free water. 

This Type 1 ultrapure water system for the laboratory is used in various sensitive analytical applications such as chromatography, LIquid Chromatography-Mass Spectrophotometry, cell and tissue culture and more critical applications


Different grades of water in the water purification system laboratory go through various processes and use various technologies to achieve a certain standard of purity and are referred to as lab purified water. Different grades of water are used in different laboratory applications. It is necessary to understand the different levels of purity and its standards to utilize it effectively in laboratory applications.
Lab Q Water provides you with the best water purification system laboratory. Lab Q ultra+ produces the Type 1 ultrapure water system for the laboratory. Lab-Q ultra Type 1 is the multipurpose lab water purifier that produces both Type 1 and Type 2 water in a single system. Lab-Q Smart-Type II  produces Type II water for general laboratory non-critical applications. Lab-Q Water maker produces Type III for general applications.

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