The quality of laboratory water is critical to experimental results, sample preparation, and other operations. There are many types of laboratory water, and choosing the right water can prevent wasted work. Water purification systems can remove various contaminants from water to produce pure water for various applications. Please ensure that the water used in your laboratory has the purity level suitable for your specific application. Continue reading to learn about the differences between various types of laboratory-grade water, common types of water used, and water purification methods.
Common contaminants in natural water
Common contaminants in tap water include gases, enzymes (such as nucleases and proteases), microorganisms (such as bacteria and viruses), organic matter, colloids, and inorganic ions. The design of water purification systems aims to effectively remove specific types of contaminants for particular applications. Key differences between various purification systems also include tank capacity, water production rate, water quality standards, system scalability, maintenance frequency, and whether remote water extraction is supported.
What are the most common contaminants in laboratory water
Common water contaminants include gases, microorganisms, enzymes, colloids, inorganic substances, and organic substances.
Organic substances (such as solvent residues, trace organic carbon)
Microorganisms (such as bacteria, viruses, and their metabolic products)
Inorganic ions (such as sodium, calcium, chlorine, nitrate, etc.)
Particulate matter and colloids
Dissolved gases (e.g., CO₂, O₂)
Enzymes and nucleic acid residues (particularly of concern in molecular biology experiments)
How does a water purification system remove contaminants from laboratory water
Laboratory pure water systems use a variety of different technologies to remove contaminants from the incoming water; each technology has different advantages and limitations. For critical applications requiring ultra-pure water, laboratories may develop multi-stage purification systems that combine multiple filtration or adsorption technologies.
How to assess and define laboratory water purity
Water conductivity
Conductivity is a unit used to measure the quality of pure water, indicating a fluid's ability to conduct electricity and reflecting the concentration of ions in the water. Water conductivity refers to the electrical conductivity of a solution between two parallel electrodes in 1 cm³ of water at 25°C, and it is also an indirect measure of the dissolved salt content in water.
Water resistivity
Resistivity is an indicator of the electrical conductivity of laboratory water. High resistivity indicates low conductivity. Resistivity can be used to measure the ion content in water and is employed to assess ultra-pure water.
Desalination Rate
The desalination rate is primarily used to evaluate the performance of reverse osmosis membranes in ultra-pure water systems. Typically, the desalination rate of Grade I RO membranes exceeds 97%.
Organic Compound Content
The concentration of carbon in water reflects the content of oxidized organic compounds in water, measured in ppm or ppb.
Biological contamination
The presence of biological contaminants such as bacteria and other microorganisms in untreated water is a common issue. Bacterial levels can be maintained at low levels through filtration, UV treatment, and sterilization solutions.
Colloidal particles
Suspended particles (such as iron, aluminum, and silica) can cause water turbidity, so they should be filtered out of laboratory water as much as possible.
TDS
TDS (Total Dissolved Solids) refers to the organic matter contained in water after removing suspended particles and colloids and evaporating the water. It is typically expressed in ppm or mg/l. A TDS meter can be used for detection, and it also reflects the ion content in the water.
Laboratory Water Purification Methods
Distillation: This is the simplest water purification method, involving boiling water in a flask connected to a cooling coil. The cooling coil condenses water vapor into liquid form, which is then collected in a separate beaker or storage tank. Distillation can remove various contaminants.
Ion Exchange: This is a gravity-driven process where water permeates downward through a vertical column filled with ion exchange resin beads. This low-cost purification method effectively removes inorganic charged ions from the incoming water but cannot remove organic compounds or microorganisms. Ion exchange is typically used as a pretreatment step before further water filtration.
Activated Carbon: A filtration process designed to remove organic molecules from the incoming water. However, activated carbon filters cannot remove inorganic ions, particles, or colloids from the water.
Ultrafiltration: Ultrafiltration effectively removes most microorganisms and particles from the incoming water. It is an effective method for removing bacteria and viruses from water. However, organic molecules and inorganic ions are not filtered out.
Reverse osmosis: Reverse osmosis removes all types of contaminants. It uses a semi-permeable membrane to remove impurities from water. Reverse osmosis is a highly effective water purification method and is relatively cost-effective.
Ultraviolet (UV) Disinfection: Utilizes short-wavelength ultraviolet light to inactivate microorganisms. In addition to killing various microorganisms, ultraviolet light (wavelength of 254 nm) can oxidize organic compounds, reducing the total organic carbon (TOC) content in water to below 5 ppb (parts per billion). However, ultraviolet light cannot remove colloids, particles, or inorganic ions from water.
Types of Water Commonly Used in Laboratories
1. Distilled Water
The most commonly used type of pure water in laboratories. Distilled water removes most contaminants from tap water, but volatile impurities such as carbon dioxide, silica, ammonia, and some organic compounds cannot be removed. Fresh distilled water is sterile, but bacteria can easily multiply after storage.
2. Deionized Water
Deionized water uses ion exchange resins to remove anions and cations from water, but soluble organic compounds remain in the water.
3. Reverse Osmosis Water
Reverse osmosis water is produced when water molecules pass through a reverse osmosis membrane under pressure to become pure water. Reverse osmosis water overcomes many of the drawbacks of distilled water and deionized water. Using reverse osmosis technology, it effectively removes dissolved salts, colloids, bacteria, viruses, bacterial endotoxins, and most organic impurities from water.
4. Ultra-pure water
The conductivity of ultra-pure water is typically below 0.055 µS/cm, indicating extremely low levels of dissolved ions and impurities. After deionization treatment, nearly all ions are removed, including cations such as sodium, calcium, and magnesium, as well as anions such as chloride and sulfate.
Types of Laboratory Water
Grade I (Ultra-Pure Water):
Grade I water, also known as ultra-pure water, is the highest purity laboratory water available. It is suitable for the most critical applications and advanced analytical procedures. This type of water has the highest purity and extremely low levels of organic and inorganic contaminants. It is typically treated using carbon filtration and RO technology. The reverse osmosis (RO) process removes nearly 95% of contaminants from the feed water.
It is suitable for high-sensitivity operations such as high-performance liquid chromatography (HPLC), inductively coupled plasma mass spectrometry (ICP-MS), and molecular and microbiological applications.
Grade II (Pure Water):
This Type II water is typically produced through a combination of reverse osmosis and ion exchange or electrodialysis (EDI) methods. It effectively removes inorganic components from the water, increasing its resistivity. Type II water is less pure than Type I water but still maintains a high level of purity. Type II water is suitable for general laboratory applications, including the preparation of culture media, pH solutions, and buffers. Its purity is lower than Type I, but sufficient to meet the requirements of many routine tasks. Type II water is typically used as pre-treatment feedstock for purification systems producing Type I water.
It can also be used for the following applications:
General laboratory practices
Microbial analysis and preparation
Electrochemistry
Flame atomic absorption spectroscopy
General spectrophotometry
It can also serve as feedwater for Type I water production.
Grade III Water
Grade III water, also known as RO water, is water produced using reverse osmosis purification technology. Among all types of pure water, it has the lowest purity and is typically used for non-critical applications such as cleaning glassware, water baths, autoclaves, and heating baths. It can also be used as feed water for Grade I and Grade II water production.
Conclusion
Understanding the specific requirements of your laboratory processes will guide you in selecting the appropriate type of water and, in turn, the appropriate water purification system. Assess your laboratory's needs for different types of water in order to select a system that will save your laboratory time and space. Some systems only provide Type 1 water, while others can complete the entire purification process to achieve the required water quality specifications.
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