Milli-Q Water

Milli-Q water is water which is cleaned using ion exchange cartridge. The process involves consecutive steps of filtration and deionization (sometimes UV irradiation also) to acquire the desirable resistivity of 18.2 MΩ cm-1 at 25°C. As a final step, this water is flowed through 0.22µm membrane filter. Milli-Q is a brand, and it is the trademark created by the Millipore corporation.  Milli-Q water can be used in PCR, sequencing, blotting, 2-D electrophoresis, mammalian cell culture, MALDI-TOF MS etc. 

Distilled Water

What makes distilled water better than deionized water? Distilled water is water that is boiled and condensed back to the liquid form. This process is known as distillation. It separates all impurities like minerals, bacteria, some viruses, and other contaminants. The second and third time distillation of the once distilled water results in double and triple distilled water. Distilled water is used in car cooling systems, laboratory experiments, certain medical devices, watering plants etc. 

Deionized Water

Deionized water means water after removal of ions. This process is known as deionization/demineralization. Ion exchange resins are used to eliminate the undesirable cations and anions such as sodium, chlorides, sulphates, silicates, calcium, copper etc. and to process the purest form of water. This water is used for laboratory applications, industry processes, extinguishing fires, cooling applications etc.  

Nuclease-Free Water

Nuclease-free water means water free from both RNase and DNase enzymes. The presence of these enzymes can degrade the molecular samples. Methods of removing nucleases include treating with DEPC (diethylpyrocarbonate), filtration, and autoclaving.  Nuclease-free water is used in applications such as PCR, sequencing, cloning, cDNA synthesis and nucleic acid purification.