How is Water Purified in the Lab？

The quality of laboratory water is crucial for the accuracy of experimental results. So, how can we obtain the required water quality?

What Kind of Pure Water does the Laboratory Need?

Various experiments are carried out in laboratories, such as chemical testing, biochemistry, and cell culture. These experiments require the use of pure water to prevent impurities in the water from reacting with reagents and affecting the experimental results. Therefore, laboratories need to purify the water quality to meet specific quality standards. According to relevant standards, laboratory water is divided into three levels:

• Type I Water： Virtually free of dissolved or colloidal ionic impurities, with extremely high purity, suitable for experiments requiring the highest purity.
• Type II Water： May contain trace amounts of inorganic, organic, and colloidal substances, widely used in biochemical and chemical experiments.
• Type III Water： Suitable for general laboratory tests and chemical analysis, mainly used for washing laboratory glassware, humidifiers, and other equipment.

Additionally, based on different production methods, laboratory water can be classified into:

• Distilled Water: Distilled water is the type of pure water commonly used in laboratories. It can remove most contaminants in tap water, but it cannot remove volatile impurities such as carbon dioxide, ammonia, silica, and some organic compounds. Therefore, the purity of distilled water is low, with a conductivity range of 0.1-0.5 µS/cm. It is usually used for general laboratory operations.
• Reverse Osmosis Water: Reverse osmosis water can effectively remove dissolved salts, viruses, bacteria, colloids, bacterial endotoxins, and most organic substances, overcoming many of the shortcomings of distilled water. High-quality reverse osmosis membranes can achieve a desalination rate of about 99%, reducing the conductivity to 0.05-0.5 µS/cm. It is widely used in various laboratory experiments.
• Deionized Water: Deionized water is further purified from reverse osmosis water to remove dissolved minerals, making it extremely low in ions and extremely high in purity. Its conductivity is usually between 0.05 and 0.2 µS/cm.
• Ultrapure Water: Ultrapure water consists only of water molecules and contains almost no ions. Its conductivity is usually 0.055 µS/cm or less. Ultrapure water is highly oxidizing and easily contaminated, so it should be used immediately after preparation to ensure the accuracy of experimental results. The standards for TOC (total organic carbon), bacteria, endotoxins and other indicators may vary depending on specific experimental requirements.

Generally speaking, ultrapure water belongs to Type I water, deionized water and reverse osmosis water belong to Type II water, and distilled water belongs to Type III water. It is important to note that all types of laboratory water are susceptible to contamination by bacteria and gases such as carbon dioxide in the air, which can lead to secondary contamination. Therefore, it is critical to maintain proper storage conditions and minimize prolonged exposure to the air.

How to Purify Water for Lab Use?

• Distiller for lab use

Deionized water is produced using an ion exchange system. In this process, water flows through a system containing ion exchange resins, and the ions in the water are replaced by anions and cations on the resins.

Laboratory deionized water systems are highly efficient, but to protect the resins, the influent water should contain low levels of oxidizing substances such as iron, manganese, organic matter, and chlorine. In addition, the resins need to be regenerated regularly, and the operating costs are relatively high.

• Reverse osmosis (RO) system for lab

In an RO  filter, water is forced through a semipermeable membrane under pressure, while impurities are retained due to the membrane’s selective permeability, ultimately producing RO water.

The RO process is energy-efficient, produces water quickly, is safe and reliable, and does not involve chemical reactions. However, laboratory RO systems require high-quality feed water, so pretreatment is required to remove large particles, suspended solids, and some dissolved contaminants. In addition, RO membranes need to be replaced regularly, and the proportion of wastewater produced is relatively high.

• Ion exchange system

Deionized water is produced using an ion exchange system. In this process, water flows through a system containing ion exchange resins, and the ions in the water are replaced by anions and cations on the resins.

Laboratory deionized water systems are highly efficient, but to protect the resins, the influent water should contain low levels of oxidizing substances such as iron, manganese, organic matter, and chlorine. In addition, the resins need to be regenerated regularly, and the operating costs are relatively high.

• Laboratory electrodeionization systems

Electrodeionization (EDI) system is an ultrapure water technology that combines ion exchange resins, ion-selective membranes and electrodialysis technology to effectively remove ions from water. The ion-selective membrane separates the resin and restricts the passage of specific ions. The water quality produced meets ultrapure water standards.

During the EDI process, an electric field acts on the ion exchange resin and membrane, driving ions to migrate from the water, through the ion selective membrane into the concentration chamber, and then out, effectively removing ions from the water. EDI systems can produce extremely high-purity water, but the inlet water quality requirements are very strict, and usually require pre-treatment using reverse osmosis or deionization systems.

Where is Purified Water Used in the Lab?

Different laboratory experiments require varying levels of water purity. Below is a brief overview of the applications for different grades of purified water:

Type I Water (Ultrapure Water):

• Electrophoresis
• Endotoxin analysis
• High-Performance Liquid Chromatography (HPLC)
• Gas Chromatography (GC)
• Mass Spectrometry (MS)
• High-sensitivity spectrophotometer experiments
• Molecular biology experiments (e.g., PCR, DNA sequencing)
• Cell culture
• Electron microscopy

Type II Water (Deionized Water, Reverse Osmosis Water):

• Preparation of buffers and media
• General chemical and biochemical analyses
• Sample dilution
• Enzyme reactions

Type III Water (Distilled Water):

• Cleaning glassware
• Pretreatment and preparation of Type I and II water
• General biochemical experiments
• Drinking water and routine analytical experiments

How to Choose Laboratory Water Purification Systems?

Selecting the right laboratory-grade water purification system requires a thorough evaluation of specific water quality needs, source water quality, system technology, capacity, budget, and supplier. For situations where water quality is poor and processing volumes are small, a distiller may be the appropriate choice. Reverse osmosis systems are well suited for medium initial and operating costs and can meet a variety of water treatment needs.

Ion exchange systems are ideal for those that require frequent regeneration; their initial cost is moderate, but operating costs are high due to the need for resin regeneration and maintenance. Electrodeionization (EDI) systems are suitable for medium to large applications that require consistently high-purity water. While EDI systems do not require chemical regeneration and have lower operating costs, they have a higher initial cost and strict requirements for influent water quality.

Faqs:

1)How is Tap Water Different from Pure Water?

Tap water can remove harmful microorganisms, suspended particles and heavy metals, but its removal rate of soluble minerals is relatively low. Tap water is mainly used to provide daily safe water. In contrast, purified water has a very low ion content and is mainly used in professional production.

2)What is the Pure Water Chemistry Formula?

Pure water chemistry is simply, H2O, which shows water is composed of one hydrogen atom and two oxygen atoms.