Demineralized or deionized water is used for many lab reactions, laboratory equipment washing, industrial processing applications and more. This water has been purified of ions, minerals, bacteria and other organics that may have been present.
Any of those contaminates can alter chemical reactions, cause scaling and corrosion for piping systems, and create a number of unique problems for specific applications. Once demineralized and deionized, water can still harm piping systems if the wrong material is specified because pure water becomes more reactive.
Learn about the use cases, qualities and preferred piping systems of purified water to keep your flow free of contaminates and your piping system running longer.
Demineralized or deionized water has been purified and neutralized. This includes removing positively charged ions (cations), like calcium and magnesium, or negatively charged ions (anions), such as chloride and sulfate.
Ideally, the end result is water completely free of any charged particles, giving the water a neutral pH, high resistivity and essentially no dissolved solids.
By using deionized water, users ensure any ions that appear in natural or tap water will not inadvertently interfere with the process. A few use cases:
Each example may require a slightly different level of purified or deionized water.
The ASTM Standards for Laboratory Reagent Water (ASTM D1193-91) defines the four different types of pure water, as shown in the chart below.
Electrical resistivity and electrical conductivity. This temperature-dependent quality quantifies the level to which water defies electricity. The more resistive the water is, the higher the purity. Greater resistivity indicates a lower level of ionic material.
pH. The pH is a measurement of water acidity or alkalinity on a scale of 1 to 14. Ultra-pure water has a neutral pH of 7.0, but is not required for Type I, II and III water because these grades of water do not have the necessary ions to be measured effectively. Resistivity and pH correlate, so resistivity can be used to identify the pH of water.
The following chart shows the relationship between electrical resistivity and deionized water.
Image credit to the Pro-Analitika Kft
Total organic compound (TOC) in parts per million (ppm). Dissolved solids include any minerals, salts, metals, cations or anions dissolved in the water. Unsurprisingly, the less TOC in the water, the more pure it is considered. At room temperature, ASTM defines the following TOC for pure water:
For comparison, fresh water may contain up to 1,000 ppm TOC, and seawater may have 30,000-40,000 ppm TOC.
Choosing the wrong piping material can have detrimental effects in different applications. Give strong consideration to piping material selection or risk it ruining chemical reactions or experiencing costly corrosion.
When determining which material to use to convey deionized water, three main performance factors should be considered:
If a material can be verified effective by those three issues, consider cost, installation and other non-application specific characteristics.
In general, plastics are known for their corrosion resistance and relative cost. A few options with various pros and cons are as follows:
In many applications, metal is the material of choice due to its familiarity. Yet, in applications where purity is a priority, some metals are prone to corrosion and leaching.
In laboratories and other purity-dependent processes, plastic piping should be strongly considered for its corrosion resistance, non-leaching properties, easy installation and related overall lifecycle costs.