Fork in a toaster. Electronics near a bathtub. A lightning strike near water. Do you recall being weary around these specific scenarios? At this point, it is common knowledge that these actions are unacceptable with the consequence of being electrocuted. This is due to the mediums (metal fork, water) having the ability to conduct electricity, or an electrical current, from the source to you. This concept is called electrical conductivity.
In this article, we will discuss the electrical conductivity of water and why it is an important parameter to understand water quality. This knowledge, and ability to test water for conductivity, will benefit any area where high water quality must be maintained: drinking water for homes, hydroponics, environmental sampling, manufacturing, to name a few.
What is conductivity in water?
To restate, the ability for a material to transmit an electrical current over a certain distance is defined as electrical conductivity, usually measured in Siemens per distance. This parameter is most intuitively understood with metals, as metal wiring is the material that provides electricity to our homes, local businesses, everything.
(Note: there are different kinds of conductivity to describe materials, but for this discussion the words electrical conductivity will be referred to as simply “conductivity.”)
Metals usually have a high conductivity, whereas plastics and household ceramics usually have a low conductivity. However, when we discuss liquids—namely water in this case—an electrolytic conductivity has the same principle, but it relies on ions in the solution to conduct electricity instead of the core material itself. Ions come in the form of salts and various other pollutants that dissociate in water to create electrically charged ions.
Pure water, or H2O, is inherently a badconductor of electricity, or it has low conductivity. This is because pure water has no solo ions with positive and negative charges floating around to allow electricity to travel. By introducing salts, chlorides, sulfides, carbonates, and other ions, the conductivity of water will increase as the concentration of ions increases. More ions, more roadway for the electricity to travel.
What affects conductivity of water?
As we just discussed, ions are the source of electrical conductivity in water, and the more ions the higher the electrical conductivity. Additionally, this material characteristic takes into account the concentration of ions, the size of the ions, and the temperature of the solution (in this case water).
Temperature also yields a direct relationship with electrical conductivity in water, as the temperature rises so does the conductivity. (Note: the opposite is true for metals!) This raises the important point of always calibrating the conductivity probe before measurement—slight temperature changes can have a noticeable effect on water conductivity. For example, common water-based solutions, and the KOH calibration solution, correlate a one-degree Celsius change with roughly a 2% conductivity change. This percentage is called the conductivity slope of the solution, similar to when calibrating pH probes.
Additionally, the type of water matters in this chat on electrical conductivity. Whether we’re talking about drinking water, natural water, processed water, or pure water, they will all have different conductivities due to the different types of ions and concentrations. The environment that the water is in will play a huge role in this factor. Pollutants can easily flow into natural water sources from runoff, and different climates can cause more or less evaporation which will change the concentration of ions. In this way, electrical conductivity can be used to classify different types of water or create benchmarks to strive for in industrial and/or consumer applications for proper quality control.
Therefore, we have 3 conductivity factors at play for common water solutions:
Concentration of ions
Type/Size of ions
The good news is that Atlas Scientific provides top-notch conductivity probes that will calculate all this for you. Note, calibration is still required.
Why is conductivity important in water?
Many industries and the overall wellbeing of the population depend on high water quality. As discussed above, water quality can be indirectly measured through conductivity—which provides insight as to how many contaminants exist in the water and have the ability to transmit electricity.
Since conductivity is usually measured in micro-Siemens per centimeter (µS/cm) or 1000 times that, milli-Siemens per centimeter (mS/cm), baseline measurements can be kept in check to maintain high-quality water with healthy conductivity levels.
To illustrate, salty seawater will have conductivity values around 50-70 mS/cm depending on the location and temperature, whereas drinking water should have conductivity values lower than 1 mS/cm. Even more so, highly sensitive manufacturing processes (semiconductors, pharmaceuticals) need extremely pure water with conductivity values under 1 µS/cm, or 1000 times less conductive than drinking water.
Therefore if conductivity values become too high, it could mean unwanted amounts of pollutants exist within the water or have recently entered the water. Excess ions contributing to higher conductivity can cause harm to household plumbing and water heaters through chemical buildup or deterioration; it can also be harmful to human and animal health if consumption occurs over extended time periods. On the other end of the spectrum, in industrial applications, the same problems can occur that could ruin expensive equipment, processes, and/or product yield.
All of these side effects can be prevented if proper monitoring of conductivity is worked into the usual routine. No matter the application, Atlas Scientific will have a conductivity probe to fit your requirements, even industrial probes that attach directly to piping for continuous monitoring.
Atlas Scientific has two different grades of the industrial probe, the K 1.0 and the K 0.1 conductivity probe. The K 0.1 should be used for applications that require a more sensitive conductivity reading (down to 0.07 µS/cm), whereas the K 1.0 will have a higher conductivity range up to 200 mS/cm.
Additionally, for consumer, environmental testing, laboratory use, or tasks that require a probing method, both mini and regular conductivity probes are available in two different ranges to accommodate all applications. The K 10 versus the K 1 yields the same concept as the industrial sensors, with the higher number corresponding to a higher conductivity range and vice versa.
(Note: this K value refers to the conductivity constant, defined by the two conductor plate’s size and distance apart within the probe. Different plate sizes and different separation distances will allow for different conductivity ranges and K values.)
In any case, there will be a probe and calibration solution setup curtailed to the specific application that will get you started with conductivity measurements. This will allow the user to detect heightened conductivity in water and subsequently provide details on the necessary action to prevent unwanted health effects and/or equipment damage.
How do conductivity probes work
Conductivity probes perform in a similar fashion as common two-prong outlet plugs. By placing two conductive plates (usually graphite or other strong, conductive metals like platinum) in the solution there will be ions in between them. The conductivity probe then applies an alternating current (AC) voltage across the conductive plates. The ions then flow to the oppositely charged panel, creating an electric current.
As we learned before, the more ions the more roadway for electricity. As a result, the strength of this current is then correlated to a conductivity value. Therefore the higher theconcentration of ions, the more ion movement (temperature increase) will increase the strength of the measured electrical current and produce a higher conductivity value.
Before actually measuring the sample’s conductivity, one must perform a calibration step to ensure the probe is aligned to the size of the conductive plates and the separation distance between them. Going back to the conductivity constant K, this plate setup determines the measurable conductivity range of the contact probe.
How to calibrate a conductivity meter/probe
First things first, calibration is extremely important to ensure a proper conductivity measurement. The bright side is that, unlike other common probes, contact conductivity probes do not need to be re-calibrated once the first calibration occurs.
As noted earlier, these contact conductivity probes have a fixed plate size, a fixed distance apart, that will never change or deteriorate throughout the probe’s lifetime. This specific setup will correlate the probe with a fixed conductivity constant K (hence 0.1, 1, 10), and therefore the probe will only be accurate in a certain range of conductivity once calibrated.
Due to this setup and K value, calibration needs to occur in the range of accurate conductivity, preferably in the middle. For example, the K 1.0 has a range from 5 to 200,000 µS/cm.
Atlas Scientific provides specific K value calibration solutions made up of different concentrations of potassium chloride (KOH) to target the K value and ranged of the conductivity probe. These highly accurate solutions will have a conductivity value on the bottle to be used during calibration.
Once the conductivity probe and calibration solution have been acquired, the first step in calibration is to simply submerge the probe into the calibration solution in the same form it would be used in testing (i.e. ensure the industrial pipe fitting is attached to the industrial probe during calibration).
It is best to have a temperature probe during calibration to ensure the solution is close to 25o C. Additionally, tilt the probe around to remove any bubbles trapped near the electrodes.
Once the probe is submerged, define the measurement with the conductivity value on the calibration solution bottle.
Now, your conductivity probe is ready to be used indefinitely.
How to measure conductivity of a solution
Once the conductivity probe is properly calibrated as discussed above, the probe can then be inserted into the solution or installed directly into the piping for a one-time or continuous measurement, respectively.
Be sure to take into account the range (or K value) of each probe so that your probe will accurately measure conductivity in the sample’s range. These probes have a generally wide range of conductivity so the exact value of the sample does not have to be known.
By understanding healthy levels of water conductivity, a baseline can be created for the specific application. Then, when conductivity values increase beyond healthy levels you will be informed to take action.
How to reduce conductivity of water
In general, this is not an easy question to answer due to the wide variety of factors that could be increasing conductivity. As we discussed above, the conductivity is increasing due to a higher presence of dissolved solids in the solution. Therefore, by removing these dissolved salts and solids, the conductivity will decrease. In other words, purification of water.
This conductivity reduction can be approached in two ways, filtration or root cause elimination.
A few different options are available to filter water for dissolved solids depending on the application and resources available.
Generally, a deionization system setup will work best to reduce dissolved solids that contribute to high conductivity. These systems can come in large scale applications to filter water before entering a household or process, or they can come in small portable systems for small scale filtration. To illustrate, the system has various resins to target positively and negatively charged ions and remove them from the water as it’s pumped through the system. Keep in mind that the larger the operation the more expensive this approach can become; it’s best to consult an expert when setting up a deionization system.
Specifically, deionization is commonly performed industrially to produce DI (deionized) water, mostly for laboratory settings, but this can be just one step in the water purifying process. Water can also go through distillation (water evaporation, collecting steam, condensing), deionizing, carbon filtration, reverse osmosis, etc, depending on the conductivity requirement of the application.
This combination of purification techniques is what leads to different definitions of water purity: purified, ultrapure, distilled, double distilled, DI. In general, conductivity will decrease with more filtration and reduce the number of dissolved solids.
Root cause elimination
This approach is more geared toward industrial applications but can be considered in the consumer world as well. This approach should be considered if conductivity values have been constantly healthy, and then suddenly skyrocket.
Rather than quickly spending tons of money on filtration, first, consider questions like “have the raw materials changed in the process? Is my water pipeline susceptible to leaching or external pollutants?” In other words, what else could have influenced this large change in conductivity? For example, the backyard pool conductivity has heavily increased. The chlorine levels may be insufficient to kill all the bacteria, or the pump has broken.
Since this is not an easy question to answer, filtration may need to be chosen, but uncovering the root cause of increased dissolved solids could save a lot of time and energy that comes with filtration.
Overall, going back to the main point of why conductivity is important in water, it allows us to monitor the water quality indirectly and to take action quickly when the water quality drops. By monitoring conductivity in any water application, significant preventative maintenance can replace large costs associated with fixing water quality.
If you are unsure exactly which conductivity and/or temperature device will best suit your needs, do not hesitate to reach out to the world-class team at Atlas Scientific.
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