Demineralization & DM Water

North Water DM Water: Ultrapure Demineralized Water

North Water is ready for all your challenges:

  • North Water makes major contributions to the development of sustainable solutions for high-quality demineralized water.
  • North Water is your go-to provider if you want to ensure sustainability while controlling costs.
  • North Water offers solutions to problems in the area of water treatment and demineralization for companies in the chemical, petrochemical, metal, food, agribusiness, energy and other sectors.

On this page:

  • What is demineralized water?
  • Demineralization
  • How is DM water quality determined?
  • Ultrapure DM water
  • Why North Water DM water?

What is Demineralized Water?

Demineralized water is water from which all salts and minerals normally found in low levels in mains water have been removed. Examples include calcium, chloride, sulfate, magnesium and sodium. Demineralized water is also known as “DM water” or “deionized water”.

You do not come into contact with DM water much in day-to-day life, other than in cleaning applications. DM water is particularly convenient in applications where you do not want to leave lime scale deposits behind, such as steam irons and car washes.

Other applications include:

  • Heating systems
  • Cosmetics
  • Aquariums
  • Fire extinguishers

However, demineralized water is used much more often in laboratories for industrial and scientific purposes, as normal mains water is unsuitable for this.


Demineralization is the process that removes minerals from water. The product produced by demineralization is DM water. Remineralization is the process of adding more minerals to water.

Various techniques are available to remove salts from water. The most common techniques for producing demineralized water are:

  • Ion exchange & deionization
  • Distillation
  • Reverse osmosis
  • Electrodialysis

Ion Exchange & Deionization

Ion exchange using special resins: positive ions are replaced with hydrogen ions and negative ions with hydroxide ions.

Water contains dissolved salts and minerals. These dissolved salts and minerals are divided into positively charged cations and negatively charged anions. Demineralization can use ion exchange to reduce these ions to very low concentrations.

Cation-exchange resin removes cations. This resin exchanges sodium, calcium and other cations for hydrogen ions (H+). This exchange produces acid that must be removed or neutralized using an anion-exchange resin.

Two different types of anion resin are used for demineralization: weakly basic and strongly basic exchangers. Both types exchange chloride, sulfide, bicarbonate and carbonate anions for hydroxide ions. In addition to this, strongly basic resin also exchanges silicic acid and silicate for hydroxyl ions. The hydrogen ions from the cation exchange, along with the hydroxyl ions from the anion exchange, constitute the final product: “pure water” (H2O).

One drawback of demineralized water is that algae can grow in the ion exchanger if not used continuously. As such, this water is not always suitable for biological or biochemical applications because it is not sterile. A distillation process is used for further purification.


The main difference between demineralized and distilled water is that distilled water normally contains fewer organic contaminants: deionization does not remove uncharged molecules, like viruses and bacteria.

Distilled water is very pure water from which distillation has removed not only all inorganic salts, but also many organic substances. Water is sometimes double-distilled (ddH2O) for optimal purity.

Reverse Osmosis

The reverse osmosis process uses a semipermeable membrane to separate dissolved solids, organic substances, pyrogens, submicron colloidal matter, viruses and bacteria from water. The process is called “reverse” osmosis because it requires pressure to force the water through the membrane, leaving the impurities behind. Reverse osmosis is capable of removing 95% to 99% of the TDS (Total Dissolved Solids) content and 99% of all bacteria, and produces safe, pure water.


Electrodeionization also includes ion exchange: an electric current is sent through the resins for continuous regeneration. The undesired ions move from the reaction surface to the electrodes.

Electrodialysis (ED) is a membrane process that uses an electric field (direct current) to transport ions through penetrable, semipermeable ionogenic membranes.

The membranes are cation- and anion-selective, meaning that they let either only positive ions (cations) or only negative ions (anions) through. A cation-selective membrane is a polyelectrolyte with negatively charged groups that can let positively charged ions through but not negative ions (repulsion).

These can be removed by a series of membranes alternating between those that let positive ions through and those that let negative ions through. Some cells will feature a concentration of ions, while ions will be removed from the cells in between. The concentrated saltwater stream is circulated until it reaches a value where precipitation can occur. At this point, the saline stream is discharged. This way, ions can be removed from the water. Uncharged particles (molecules) cannot be removed from the water using this method.

Cation-selective membranes are made from sulfonated polystyrene, and anion-selective membranes from polystyrene with quaternary ammonium groups. It may be necessary to pretreat the water before electrodialysis. Suspended solids greater than 10 µm will have to be removed because they can clog the pores. In addition, some substances neutralize membranes, such as large organic anions, colloidal matter, iron oxide and manganese oxide. Possible pretreatment methods include active charcoal filtration (organic substances), flocculation (colloidal material) and filtration.

How is DM Water Quality Determined?

Water naturally conducts electrical currents due to the presence of positive ions (cations) and negative ions (anions). This is called conductivity and is expressed in Siemens per meter. For greater accuracy, the unit typically used is micro-Siemens per centimeter (µS/cm). Drinking water normally has a conductivity of between 300 and 800 µS/cm.

Because DM water does not have many ions, it has low conductivity. DM water does not have a defined level of quality. In practice, water is considered to be of DM quality if its conductivity is less than 5 µS/cm. Most commonly however, its conductivity is less than 0.2 µS/cm. Values lower than this are no longer expressed in conductivity, but rather in resistivity. Resistivity is the reciprocal quantity (1/x) of conductivity (0.2 µS/cm = 5 MΩ). Water is considered ultrapure at values exceeding 18 megaohms.

North Water: Only the Purest DM Water

To obtain demineralized water, North Water uses techniques such as membrane filtration and ion exchange. Thanks to its ultrapure quality, North Water DM water offers good conductance and prevents contamination in expensive machinery. Our DM water is used in the chemical, energy and food and beverage industries.

Quality and Cost-Effectiveness

With DM water, our focus lies on reliability and supply security. Naturally, the best product ultimately ensures the most stable and thus also cost-effective processes. We guarantee a high degree of reliability and a sustainable supply.

Why North Water DM Water?

  • Ultrapure quality
  • Sustainable solutions
  • Innovative technologies
  • Service & all-in-one solutions

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