Laboratory Water Purification Buying Guide

Water image

Water is used in almost every aspect of the lab’s operation, from simple washing of glassware and feed water for lab equipment, to preparing solutions for more specialized experiments, such as HPLC and PCR. Purified water is indispensible in the laboratory; it is therefore important to choose the best water purification system for your needs.

There are a number of ways to purify water so that it meets the purity requirements for specific uses. This Buying Guide will take you through the different options you have, and explain the important things you need to consider before deciding on a water purification unit for your lab.


The first thing you need to consider is the intended use(s) or application(s) of the purified water. Will you use the water solely for specific experiments? What are these experiments? This is important because some experiments have particular water requirements. (For example, some experiments require nuclease-free water.)

What analytical instruments will it be used for? Will it also be used for more general purposes in the lab, such as feeding a dishwasher, autoclave or water bath? It is common to have multiple intended uses for water in a laboratory.

It is important to evaluate the water quality requirements for the different applications in your lab. If there are multiple uses for the purified water, it is likely that there will be different water quality requirements. The quality of lab water is determined by the level of contaminants present. Water contaminants are typically classified into five main groups, as shown in Figure 1. These contaminants affect experiments in different ways.

Figure 1. The five main groups of water contaminants and examples of how they affect lab experiments.

Water Purification Image 1

The degree of water purity is indicated by its type or grade, and is indicated by several parameters. Figure 2 shows the commonly used lab water quality parameters.

Figure 2. Lab water quality parameters

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Manufacturers of laboratory water purification systems classify laboratory water as Type I, II, and Type III. This terminology (Type I, II, III) is familiar to laboratories, and will be referred to in the rest of this Guide. Figure 3 lists typical uses and applications of these different water types.

Figure 3. Types of lab water and their typical uses/applications

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(Note: Process definitions of purified water are also used inaccurately to designate water quality, such as RO water (reverse osmosis water), DI water (deionized water), and distilled water (water purified by distillation). These process definitions of water do not adequately define water quality.)

Because water is used in a wide range of tasks in the lab, it is not unusual that you might require more than one water quality for your lab.

Buying Guide Tip: If your lab needs more than one type of water, some vendors have systems that produce two water types from a single system, e.g. Type 3 and Type 1, or Type 2 and Type 1 water from a single unit (at different dispensing points).

Several professional organizations have detailed published or proposed standards for water quality, such as ASTM, CLSI, CAP, ACS, ISO, USP, and EU. If any of the applications in your lab must adhere to the standards required by these organizations, make sure that the water purification system you are purchasing meets the specifications of the standard.

Buying Guide Tip: Some experiments have special water quality requirements, such as nuclease-free for PCR, extremely low ionic contaminants for trace ion and elemental analyses, and very low organic contamination in trace organic analyses by LC-MS. Some vendors have dedicated water purification systems for 'sensitive' applications such as these, or they may have application-specific, point-of-use polishers that can be connected to their polishing system to produce such application-specific Type I water.


It is important to consider the amount of water used in your lab, and to buy a system that matches your needs. The quantity of water required should be based on when your water demand might peak, instead of total consumption levels over a period of time (daily, weekly, etc). For example, a system may be able to deliver the total volume of purified water required for a day, but it may not be able to generate the volumes of water required during peak times, such as the filling cycle of a lab glassware washer.

Also, think of your future water needs. It may be wise to future-proof your lab by buying a system that slightly exceeds your current requirements, allowing you to cope should there be an increase in demand for pure water in the near future.

Buying Guide Tip: Make sure your water system is not oversized. In the same way that you need a water system that is large enough to deliver the volume you need, it also should not be any larger than necessary. Oversized systems will take up more space, and will allow the purified water to be stored for longer periods, which increases the chance of bacterial contamination.


There are several methods of delivering the different types of water. Type III water can be produced by a single purification method/technology, whereas Type II water may use a combination of methods. Type I water is produced by combining several technologies, usually by a two-step process: producing Type II or III water from tap, then further purification (polishing) of the purified water using a series of technologies. Figure 4 shows how the different types of water can be produced.

Figure 4. Different methods for producing Types III, II, and I water.

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  • Distillation is the oldest method of water purification, and removes a broad range of contaminants. Distillation can only produce Type III water, or Type II at best. Organic carryover and the necessity to store the distilled water introduces contaminants back to the purified water.
  • Reverse osmosis (RO) is capable of removing the bulk of a wide range of types of contaminants, typically 90-99% inorganic ions (depending on charge and size), organics, and virtually all colloids, microorganisms, endotoxins and macromolecules. Although extremely effective as a purification technology, the RO process operates relatively slowly, so the purified water from RO systems is usually supplied with separate pure water storage tanks. Similarly, depending on the nature of the feedwater, it may be necessary to pre-treat the feed stream to protect the RO membrane, especially in areas where feedwater has high levels of organic contamination, hardness and free chlorine.
  • Deionization (DI) uses ion exchange resins to remove ionic contaminants in water. Two common systems that use deionization are:
    (1) Disposable ion exchange cartridges use specially developed color-change resin beads that change color as they become exhausted, indicating that the cartridges need to be changed.
    (2) Service deionization (SDI) systems and water treatment media are contained in portable tanks of various sizes. The tanks may contain cation exchange resin, anion exchange resin, mixed bed resins, and sometimes, granular activated carbon. When the water quality drops below the set point, the tanks are swapped for tanks with freshly regenerated ion exchange resin that has been processed off-site.
  • Reverse osmosis and deionization (RO-DI) combination will allow you to achieve higher levels of purity compared to RO or deionization alone. RO removes bulk of the contaminants, and adding deionization will further remove the ions that are left behind after RO.
  • Reverse osmosis and electrodeionization (RO-EDI) combination will produce Type II water on a consistent and reliable basis. The ion exchange resins in the electrodeionization module are continuously regenerated, without the need for chemical regeneration and the disadvantages associated with it.

Table 1 lists the benefits and advantages of the different methods used to produce Type II and III water.

Buying Guide Tip: Type II or III water is used as feed water for Type I water systems. The performance of a Type I water system, and the quality of water it produces, relies heavily on feedwater. It is therefore critical that you make a good decision about your Type II or III system if it is to be used to produce Type I water.

Table 1. Benefits and weaknesses of water purification methods that produce Type II and III water

Purification Method




Removes broad range of contaminants; low capital cost; does not require filters or cartridges, eliminating concerns on consumables (longevity, shelf-life or a need to maintain stock).

Slow process; uses a considerable amount of energy and water; requires periodic heater changes; depending on the quality of feed water, requires periodic cleaning with strong acids and may necessitate the use of pretreatment; low resistivity water; organic carryover.

Reverse osmosis (RO)

Removes broad range of contaminants; economical; minimum maintenance.

RO membrane prone to fouling, plugging; produces only Type III water.

Disposable ion exchange cartridges (disposable deionizers)


Removes ions; a cost effective option for producing small volumes of purified water on demand; easy to use.

Prone to organic fouling especially if the feedwater contains a large concentration of dissolved organics; does not remove organics; particulate contamination from tiny fragments of the stagnant water in the cartridges could cause excessive bacterial growth; expensive if using large volumes of purified water.

Service deionization systems (SDI)

Efficiently removes ions; easy to use; low capital cost.

Chemical regeneration generates organics and particles; prone to organic fouling, especially if the feedwater contains a large concentration of dissolved organics; does not remove organics; particulate contamination from tiny fragments; stagnant water in the tank could cause excessive bacterial growth.

Combination of reverse osmosis and deionization (RO-DI)

Higher purity than RO or deionization alone.

If the deionization process uses SDI, all the disadvantages (listed above) are also true for RO-DI.

Combination of reverse osmosis and electrodeionization (RO-EDI)

Higher purity than RO or deionization alone; no chemical regeneration; high water recovery; low maintenance; low operating cost; no particulate or organic contamination.

Stringent requirements for the quality of feedwater (RO water).

Buying Guide Tip: In many cases, Type II and III water need to be stored in a reservoir. To avoid or minimize bacterial contamination of the purified water, have a germicidal UV lamp installed in the reservoir.

  • Producing Type I water involves a two-step process:
    (1) Producing Type II or III water from tap water
    (2) Polishing Type II or III water using an efficient combination of technologies that will further remove contaminants. These technologies are listed in Figure 5.

Figure 5. Technologies used to polish Type II and III water to produce Type I water

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There are two basic options for the production of Type I water, as illustrated in Figure 6. There are water purification systems that contain all the technologies to purify tap water to Type II or III, and the technologies necessary to polish this Type II or III water to Type I, in a single unit. On the other hand, Type I water can be obtained by having two separate systems: the first system purifies tap water to Type II or III, and the second system feeds from the product water of the first system (polishing system) to produce Type I water.

Figure 6. Options for the production of Type I water

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Buying Guide Tip: When buying a Type I water system, determine the source of feedwater you will use. There are Type I systems that feed directly on tap water. If you have an existing source of Type II or III water, you may opt to purchase just a polishing system. But consider how reliable this existing source of Type II or III water is. Has the system it broken down before? Does it have a history of contamination? Remember, the quality of Type I water depends a lot on the feedwater. Also, if the feedwater gets heavily contaminated, the Type I system might get so contaminated that it will need replacement.


There are a number of configurations to provide purified water throughout a facility. The choice depends on the unique needs that have to be met. Below are some configurations:

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A central system is useful when the entire facility has the same water quality requirement. An example is the clinical laboratory in Sao Paolo, Brazil, which uses 1,000 L/hr of purified water for its clinical analyzers.

Water Purification Video Image 1

The advantages and disadvantages of the different configurations must be taken into account before making a decision.

Table 2. Some advantages and disadvantages of the different water purification system configurations for a facility




Central, multiple make-up systems (one loop)

·      Only one system to maintain.

·      Lower initial investment.

·      General system maintenance requires all labs to stop using water.

·      If the loop becomes contaminated or the system fails, then the entire facility is without water.

·      Risk of drop in water quality if distribution loop is long.

Floor-by-floor (departmental)

·      Can accommodate varying water quality and volume needs.

·      Each department floor has some control over its water supply.

·      High initial investment

·      Reduces the risk of a total facility shut down, because if one system is down, others are still operational.


Point-of-use systems

·    Eliminates the need to extend central piping to all departments, and the downtime associated with contamination and maintenance procedures.

·    Labs have total control of their water quality.

·    Higher investment, especially if all labs are in close proximity to each other.

·    Eliminates risk of facility shutdown because of water quality issues.


·      Can accommodate varying water quality and volume needs.

·      Risk of loop contamination and downtime.


Feedwater is critical to a water purification system’s performance. Make sure the feedwater requirements of the water system are met. If the system feeds on tap water, and the tap water does not meet the specifications set by the purification system manufacturer, pre-treatment might be necessary. For example, very high organic load in the tap water will require activated carbon to bring it down to acceptable levels.

Ease of use
How easy is it to use the system? Many systems today have remote dispensing options that allow delivery of purified water some distance from where it is generated, with monitors on the remote dispenser allowing you to check the quality of water that is being dispensed. Some systems have volumetric dispensing options, which could be quite convenient.

Maintenance requirements
Does your laboratory have someone who oversees the maintenance of the water system? The system’s performance depends on proper maintenance. Parts and cartridges have to be replaced; some systems require regular sanitization. Are the parts and cartridges easy to replace? Maintenance of the system should be as easy as possible, allowing for minimal downtime. New systems may have built-in alarms and calibrators that warn if certain components are coming to the end of their lives.

Buying Guide Tip: Depending on your budget, some manufacturers will offer aftercare maintenance as part of their deal or be able to advise you on what you can do by yourself. Whichever system you choose, make sure the water is circulated regularly, as moving water stays purer for longer, especially when considering biological impurities.

Availability of parts/supplies, accessories
Make sure parts and accessories are easily obtainable.

Regulatory guidelines
Some manufacturers offer programs to facilitate validation procedures, deliver certificates of calibration, or offer features ensuring full regulatory compliance. If you are concerned about traceability, you can select a system that stores a history of key information, or that allows remote access to the system status and water quality parameters through an internet browser. An example is the Millitrack® Compliance e-Solution from EMD/Merck Millipore.

Environmental impact
Carefully consider the technologies used; compare the electricity and water consumption. What is the frequency of cartridge replacement? Some manufacturers have cartridge return programs and recycle the exhausted DI modules. Consider a system that uses electrodeionization (EDI); it uses small quantities of ion exchange resin that are rapidly and continuously regenerated, avoiding the environmental impact of chemical regeneration associated with service deionization.

Consider the initial investment and total cost of ownership. How much water goes to waste? What will be the power consumption? Also consider the cost of consumables.

Some vendors will accommodate your space/footprint requirement with their flexibility in installing systems on floors, walls or under a sink etc, or a remote dispenser(s) on the bench.

System features you might consider:

  • In-line resistivity monitor: This gives you a numerical value of the resistivity of the water being produced or dispensed, instead of just a green/red light (green – resistivity is within specification; red – resistivity is below specification).
  • In-line TOC monitor: Shows the TOC level of the water being dispensed.

Buying Guide Tip: If organic contamination is critical for your applications, it is best to get a system with in-line TOC monitor, and not just rely on the resistivity of the water. There is no correlation between ionic contamination (indicated by low resistivity) and organic contamination. Water that has resistivity of 18.2 MΩ.cm does not necessarily mean it has low TOC.

  • Alarms/reminders for maintenance and consumables replacement. Rather than just warning lights, you may need indicators that tell you what specific component needs to be replaced.
  • Remote dispenser, which frees bench space.
  • Ability to track/record water usage and quality with a built-in software. This would be useful for those who work in a regulated environment.


Water purification systems continue to improve as developments in analytical instrumentation make it possible to routinely detect and measure trace and ultratrace levels of analytes. With the emergence of new contaminants in tap water, such as pharmaceuticals and personal care products, scientists are seeking to develop water purification systems that can remove these. Manufacturers of lab water systems are investigating if their current product offerings are able to eliminate these contaminants, or if the existing water purification processes need to be modified. As new analytical and molecular biology technologies are introduced in laboratories, lab water purification system manufacturers will make sure they can produce water to meet specific water quality requirements. In an effort to be environmentally responsible, many vendors are making sustainability an integral part of their business.

Water is an essential part of the laboratory. Your success depends on good water. To help you choose the correct system, use the SelectScience product and supplier directory for an overview of systems, download application notes and technical information and read user reviews from other SelectScience members. You can also watch a webinar on minimizing contamination risk in ICP-MS and LC-MS/MS analyses by using ultrapure water.

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To help you choose the correct system, use the SelectScience product and supplier directory for an overview of systems, download application notes and technical information and read user reviews from other SelectScience members.

View all information about water purification here.