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How Water Contaminants Impact Lab Analyses

How Water Contaminants Impact Lab Analyses

Water is known to harbor a range of contaminants that can potentially impact lab experiments.

Erica Tennenhouse, PhD

Erica Tennenhouse, PhD, is the managing editor of Clinical Lab Manager.

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There are many ways to ruin an experiment. Incorrect labels, misread protocols, measuring mishaps, data errors, and flawed research design all can turn an otherwise decent experiment into a big waste of time and resources.

Contamination is another common source of experimental error. Coughing or breathing into a petri dish, failing to wipe down the work area, and touching a pipette tip are all sure ways to introduce contaminants into your experiment. In addition, water is known to harbor a range of contaminants that can potentially impact lab experiments. Because water is so pervasive in laboratory processes, it is important to know what’s in your water, how it can impact your experiments, and how to get rid of contaminants.

The culprits

On its website, MilliporeSigma (Burlington, MA) outlines five major classes of water contaminants: gases, bacteria and their by-products, inorganic ions, organics, and particulates and colloids. The following are brief summaries of the impacts these contaminants can have on laboratory experiments:


Water contains dissolved gases such as nitrogen, oxygen, and carbon dioxide. Ammonia and carbon dioxide can be ionized to form weak acids and bases, which change the pH of the solutions they are in; even a slight alteration in pH can inhibit a desired reaction. Nitrogen gas can also form bubbles that block optical sensors of spectrophotometers and hinder particulate counting.

Bacteria and their by-products

It is not only the bacteria in water that can interfere with experiments, but also the compounds they release. Bacteria and their by-products can contaminate cell cultures and prevent cell growth. Endotoxins, DNAses, RNAses, and proteases can make DNA and RNA unstable in a polymerase chain reaction (PCR) and microarrays.

Inorganic ions

In water, inorganic ions such as sodium, calcium, magnesium, zinc, and sulfate can affect biochemical reactions by acting as catalysts, inhibit enzyme immunoassays, and interfere with colorimetric methods. Certain ions, such as phosphate, can also bind to DNA or RNA, and heavy metals are toxic to certain cell types in cell culture.


Naturally occurring and human-made organic compounds can be found in water. Naturally occurring contaminants include fulvic acids, humic acids, and tannins originating from plants, while human-made contaminants are from detergents, solvents, oils, pesticides, and other sources. These contaminants can interfere with experiments by aiding microbial growth, increasing background noise, and fouling media.

Particulates and colloids

Particulates—including vegetable debris, sand, and rock—and colloids in lab water can potentially interfere with many assays and instruments. For example, particulates can damage high-performance liquid chromatography (HPLC) pumps and injectors and increase back pressure in the system.

Keeping water clean

To avoid the negative impacts of water contaminants, a water purification system is required. Which system a lab should choose depends on the level of purification required for the instruments in the lab and experiments being run. Type III water is the most common grade and is typically used to supply equipment like glassware washers and autoclaves. Type II water is used primarily for making buffers, in culture media, and for preparation of reagents for chemical analysis. Type I (ultrapure) water is used for analytical techniques including HPLC, gas chromatography, and inductively coupled plasma mass spectrometry; molecular techniques like PCR and sequencing; and preparation of media for mammalian cell culture and in vitro fertilization.

Though there are many potential sources of error in any given lab experiment, impure lab water doesn’t have to be one of them. By knowing which contaminants might impact your instruments and experiments and selecting the appropriate water purification system for your lab, you come one step closer to obtaining high-quality, robust results.

For additional resources on water purification, including useful articles and a list of manufacturers, visit