Water in the lab is not all the same—what a huge difference there is!

Water may seem ordinary in the lab, but it is an invisible key that determines the success or failure of experiments. You might think all lab water is more or less identical, but that’s far from the truth. From basic cleaning to ultra-high-precision testing, different experiments have vastly different requirements for water in terms of purity (ion and organic matter content), sterility (microbe content), and nuclease-free properties. Even a tiny deviation in water quality can ruin your well-designed experiment. Today, we’ll walk you through the ins and outs of various types of lab water.

I. Water for basic cleaning and pre-treatment

Tap water source & characteristics: It is the daily municipal water supply, containing various minerals, ions, organic matters and microorganisms.Usage: It is only used for non-experimental operations such as laboratory bench cleaning and floor washing. Even when cleaning labware, a purer water is required for the final rinsing.

Deionized water preparation & characteristics: Most anions and cations in water are removed via ion exchange resins, yet it may still contain organic matters, microorganisms and particles.Usage: Preliminary cleaning and final rinsing of glassware, as well as preparation of general reagents with low purity requirements.

II. Water for routine experiments and reagent preparation

Reverse osmosis water preparation & characteristics: It is produced by filtration through reverse osmosis membranes, which can remove the vast majority (usually >90%-99%) of ions, organic matters, microorganisms and particles. As a cost-effective purification method, it is one of the primary technologies for producing pure water in laboratories.Usage: Preparation of routine chemical reagents, water supply for biochemical analyzers and chemical analyzers, and also serving as the feed water for higher-purity water (e.g., ultrapure water).

Ⅱ. Water for Routine Experiments and Reagent Preparation

Reverse osmosis water preparation & characteristics: Purified via reverse osmosis membrane filtration, it removes most (typically >90%-99%) ions, organic substances, microorganisms and particulates. As a cost-effective purification method, it is one of the core technologies for laboratory pure water preparation.Applications: Preparation of routine chemical reagents; feed water for biochemical and chemical analyzers; also serves as the inlet water for higher-purity water (e.g., ultrapure water).

Distilled water preparation & characteristics: Obtained through heating evaporation and condensation recovery, it effectively removes ions, non-volatile organic compounds and microorganisms, but may contain volatile organic substances and dissolved carbon dioxide.Applications: Preparation of general chemical reagents; base water for cell culture-related reagent preparation (needing subsequent sterilization); common PCR experiments, etc.

Ⅲ. Water for high-precision analysis and biological experiments

Ultrapure water preparation & characteristics: Usually using RO water or distilled water as raw material, it is purified by the combination of multiple technologies (e.g., ion exchange, EDI, ultraviolet oxidation, ultrafiltration, etc.) and represents the highest-purity water. Its resistivity can reach 18.2 MΩ·cm (25°C), removing almost all ions, organic substances and particulates while effectively controlling microbial levels.Key Note: Ultrapure water pursues ultimate purity, but it cannot guarantee absolute sterility if no sterile filter membrane is equipped at the water outlet.Applications: Ultra-high precision instrumental analysis such as high performance liquid chromatography (HPLC), inductively coupled plasma mass spectrometry (ICP-MS) and atomic absorption spectrometry (AAS); base water in molecular biology experiments (e.g., preparation of nuclease-free water); substrate for cell culture water (needing subsequent sterile filtration).

Sterile water preparation & characteristics: Refers to water subjected to sterilization treatment (e.g., autoclaving, sterile filtration). Its purity depends on the raw water. For instance, sterile filtration of ultrapure water yields sterile ultrapure water, while sterilization of deionized water produces sterile deionized water. Applications: Preparation of microbial culture media, sterile cell culture, and all biological experiments requiring a sterile environment. Note: Cell culture requires both sterility and high purity, so sterile water must be prepared with high-purity water (e.g., ultrapure water, double-distilled water).

Nuclease-free water preparation & characteristics: Specifically refers to high-purity water (usually ultrapure water or double-distilled water) that has undergone treatments (e.g., DEPC treatment, ultraviolet irradiation) to remove or inactivate nucleases (RNase, DNase).Applications: All nucleic acid-related experiments including RNA extraction, RT-PCR, qPCR and molecular cloning must use nuclease-free water to prevent nucleic acid degradation.

Ⅳ. Liquids for special experiments (non-pure water)

TE Bufferkey difference: It is not pure water, but a buffer solution prepared from chemicals such as Tris-HCl and EDTA.Applications: Specifically used for dissolving and storing DNA/RNA. It provides a stable pH environment and chelates metal ions to inhibit nuclease activity and prevent nucleic acid degradation.

Summary:

Selecting the right experimental water is the first step to a successful experiment. When making a choice, it is essential to clarify the core requirements of the experiment:

Concerned about instrument background signals? → Prioritize purity (ultrapure water).

Concerned about microbial contamination? → Prioritize sterility (sterile water).

Concerned about nucleic acid degradation? → Prioritize nuclease-free property (nuclease-free water).

It is recommended to verify the water quality standards against your needs before the experiment to avoid rework caused by improper water use. Ensure every operation is accurate and efficient, laying a solid foundation for reliable experimental results.