Double distilled water

Purified water is water that has been mechanically filtered or processed to remove impurities and make it suitable for use. Distilled water has been the most common form of purified water, but, in recent years, water is more frequently purified by other processes including capacitive deionization, reverse osmosis, carbon filtering, microfiltration, ultrafiltration, ultraviolet oxidation, or electrodeionization. Combinations of a number of these processes have come into use to produce water of such high purity that its trace contaminants are measured in parts per billion (ppb) or parts per trillion (ppt). Purified water has many uses, largely in the production of medications, in science and engineering laboratories and industries, and is produced in a range of purities. It can be produced on site for immediate use or purchased in containers. Purified water in colloquial English can also refer to water which has been treated ("rendered potable") to neutralize, but not necessarily remove contaminants considered harmful to humans or animals.

Purified water is usually produced by the purification of drinking water or ground water. The impurities that may need to be removed are:

Distilled water is produced by a process of distillation and has an electrical conductivity of not more than 11 µS/cm and total dissolved solids of less than 10 mg/litre. Distillation involves boiling the water and then condensing the vapor into a clean container, leaving solid contaminants behind. Distillation produces very pure water. A white or yellowish mineral scale is left in the distillation apparatus, which requires regular cleaning. Distilled water, like all purified water, must be stored in a sterilized container to guarantee the absence of bacteria. For many procedures, more economical alternatives are available, such as deionized water, and are used in place of distilled water.

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