A Complete Guide to Deionised Water

There are many types of purified water. In our Complete Guide to Deionised Water, we’ll explore what it is, how it’s made, its uses, benefits, and specifications. You’ll also find further information and reading material in the links at the bottom of this page, and of course you can buy deionised water from ReAgent, one of the UK’s leading deionised water suppliers. 

What Is Deionised Water?

Tap water normally contains ions which have come from the soil, such as sodium and calcium; and from water pipes, such as iron and copper.

Deionised water (often abbreviated to DI water) is quite simply water which has had these ions removed through a filtration or deionisation process. Ions are atoms and molecules which have an electric charge because they have gained or lost electrons. Deionized water is almost pure H2O; it contains no ions which means it has no charge.

Deionised water has a wide range of uses in many industries and is manufactured on an industrial scale by deionised water suppliers using one of several deionisation processes.

How Is Deionised Water Made?

Deionised water is made through a process called deionisation. This is a chemical process using specially manufactured ion exchange resins. These resins are both positively (cation) and negatively (anion) charged and in effect remove their respective ions from the water passing through them.

Ion exchange resins are made from organic polymer chains that form porous plastic beads. These beads are positively or negatively charged, and it is this that attracts the ions before replacing them – this is what is called ion exchange.

There are three types of deionisation: counter-current, co-current and mixed bed.

Counter-current deionisation

Counter-current deionisation occurs in two ways: either water enters from the bottom of a cation or anion ion exchange column and regeneration chemicals from the top, or vice versa. This is a quick, high quality and cost-effective method of deionisation.

Co-current deionisation

In co-current deionisation, both water and regeneration chemicals enter at the top of the cation or anion column and exit at the bottom. This is a higher cost option as more regeneration chemicals are used than during the counter-current deionisation process. The result is also slightly lower in purity.

Mixed bed deionisation

Mixed bed deionisation is an equal mixture of cation and anion resin combined into one ion exchange column, and produces the purest form of deionised water. It is an expensive and complex process that is normally only used when very high purity water is required.

How Do You Know If Deionisation Has Worked?

We know that ions conduct electricity which means we can measure the ions in water by running an electric current through it. The fewer the ions, the lower the conductivity levels. That means there should be little to no conduction in deionised water.

Uses of Deionised Water

Deionised water has various uses and has applications in a wide variety of industries.

Lab Tests

Chemical Analysis through a MicroscopeLab experiments often require high purity deionised water because if water which contains ions is used, these ions can switch places with other ions you may be using in your test, causing it to fail or produce false results. Deionised water is also used to clean laboratory equipment, because it will not taint it as tap water would.

Domestic Cleaning

Deionised water ‘wants to’ absorbs ions because it has been stripped of its own. These ions can include the minerals and contaminants found in dirt, which makes deionised water an effective cleaning agent. It’s especially effectual on surfaces such as windows, wood and mirrors because it doesn’t leave a residue. You can also use deionised water to wipe down surfaces you’ve cleaned with a different solution for the same reason.

Motor Vehicles

Deionised water is commonly used in engine batteries and coolant systems as the water’s high purity extends their lifespan. If ordinary tap water was used, the battery wouldn’t last as long and the coolant system may overheat. Deionised water is used because it is a poor conductor of heat.

Cleaning Archaeological Material Collected From Underwater Sites

Archaeologists use deionised water to remove chlorides from artefacts they have collected from underwater archaeological sites. It can also be used to clean these artefacts in staged baths.

Using Deionised Water to Extinguish Fires

Deionised water is used in fire extinguishers again because it is such a poor conductor. It conducts electricity very badly and is therefore safe to use to extinguish an electrical fire. At the same time, it won’t damage electrical equipment as much as regular water.

Fish Tanks

Healthy clown fish swimming in waterDeionised water is used in fresh water fish tanks due to its high purity. Using unpurified tap water leads to algae build-up which is harmful to marine life. Deionised water minimises algae growth and helps fish stay healthy.

Cosmetic Products

Once again due to its high purity levels, deionised water is used as an ingredient in cosmetic and beauty products as it extends their shelf life. Using ordinary water would not be as effective as it contains too many impurities which make it an unviable product for use in the cosmetic industry.

Industrial Machinery

Deionised water is used to clean, cool and lubricate industrial machinery, as well as being used as an ingredients to make certain industrial products. Deionised water won’t corrode machinery during the cleaning process as ordinary water would. It also prevents rust and the build-up of minerals such as salt.

Benefits of Deionised Water

The benefits of deionised water are very closely related to its uses. Benefits include:

  • High purity
  • Non-corrosive
  • Low conductivity
  • Leaves no residue
  • Does not build up scale
  • Good diluter
  • Quick to manufacture

Can You Drink Deionised Water?

Some people do drink deionised water, believing it to be healthy because of its high purity. However, we do not recommend drinking deionised water – especially deionised water made to an industrial grade. Industrial grade deionised water is definitely unfit for human consumption.

Drinking water from a glassDeionised water tastes and feels unpleasant in your mouth, and there are also other reasons it’s not fit for consumption:

  • You won’t get the minerals found in ordinary water, such as calcium and magnesium, that your body needs
  • If you use deionised water for cooking, the water will absorb the nutrients from your food. When you boil vegetables, for example, the nutrients you need will be in the water you throw away rather than in the vegetables you eat
  • When deionised water comes into contact with other materials, it wants to absorb their ions. If deionised water has come into contact with other chemicals or metals, they may be in the water you drink – this may lead to a risk of metal toxicity. This is especially true if you drink deionised water from a tap
  • In the same way, if you drink deionised water it may absorb ions such as calcium and magnesium from the tissues in your body
  • Deionised water doesn’t quench thirst as well as ordinary water
  • There is evidence that drinking deionised water directly causes adverse effects to the body’s metabolism, intestinal mucous membrane, and that it may cause organ damage in the long term

Our conclusion: deionised water has better uses in industry, technology and the laboratory than it does for humans. Please do not drink it.

Hazards Of Deionised Water

Deionised water doesn’t pose any hazards in normal industrial use, including physical, health or environmental hazards. It is not flammable, it’s stable, and no classified risks have been identified.

But as we’ve just seen, deionised water can be harmful if you choose to drink it. Please don’t! Deionised water is best used for industrial purposes only.

Deionised Water Specification

H₂OM.W. 18.01
pH @ 20°C5 – 8
Conductivity can increase on storage as CO2 can be absorbed.

Deionised Water Material Safety Data Sheet (MSDS)

Deionised water is not classified and therefore does not require a material safety data sheet, but we do provide a deionised water safety data sheet as advice for product users. Under REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals manufactured in or imported into the E.U.), material safety data sheets (MSDS) are referred to as safety data sheets (SDS).

Where To Buy Deionised Water

You can buy deionised water from a variety of places. Of course we believe ReAgent is the most suitable!…but there are different types of customers and businesses for whom we won’t be the most appropriate deionised water supplier.

Businesses Buying Deionised Water

Buying chemicals online from ReAgent's Chemical ShopIf you are a business looking for a recognised, reputable chemical company, a manufacturer such as ReAgent will be able to help. Why?

  • Reliability is a top priority – you don’t want to order a tanker of deionised water only for it to be late or off-spec
  • An established company has a proven track record and thousands of happy customers (ReAgent was established over 40 years ago)
  • A chemical manufacturer is an expert and probably supply a range of high purity waters
  • You will get advice on the best type of water for your needs: a different type of purified water may be more suitable
  • With ReAgent, you’ll get offer free technical support before you buy, plus after-sales support
  • Chemical companies often have quality accreditations – at ReAgent we hold ISO 9001 and ISO 14000
  • Reliable couriers mean your order will be delivered on time and in full
  • Ask about certificates of conformity and analysis if you needed
  • Making to order means a higher quality deionised water product than off the shelf sources
  • You can create an account and place regular orders easily

However, many chemical companies we don’t supply deionised water direct to consumers. This is the case at ReAgent, where we only supply chemicals to businesses.

Consumers Buying Deionised Water

As a consumer, you can buy deionised water from many large supermarkets and hardware stores. The benefits are ease and cost – you will find deionised water cheaper if you purchase in small quantities from these retailers, you can include the product in your weekly shop and it’s suitable for use in your steam iron and vehicle battery.

However, as this type of deionised water isn’t made to order, the quality and conductivity probably won’t be as good. Plus it’s only really suitable for when you need to buy a very small quantity.

You can also purchase deionised water from online retailers such as Amazon and eBay. If you choose to do this, we recommend checking the sellers in detail. You’ll probably find that they aren’t of as such good repute as established chemical companies. For example, they generally won’t have the same high quality standards or accreditations.

Buying deionised water online also means there’s another party in your supply chain, which can get complicated. It may be difficult to get a VAT receipt, and you probably won’t get the same standard of after-sales support.


The content on chemicals.co.uk and everything published on it is provided as an information resource only. The content, its authors and affiliates accept no responsibility for any accident, injury or damage caused in part or directly from following the information provided on this website. We do not recommend using any chemical without first consulting the Material Safety Data Sheet which can be obtained from the manufacturer and following the safety advice and precautions on the product label. If you are in any doubt about health and safety issues please consult the Health & Safety Executive (HSE).