What is conductivity?
Conductivity is how we measure the ionic content (such as chloride, nitrate, sulfate, sodium, magnesium, calcium, or iron) in a body of water by measuring the water’s ability to conduct electricity.
Why is conductivity important?
Every body of water has its own unique conductivity level, based on its bedrock. It is important to establish a baseline as some bodies of water have naturally high levels due to their geology and geography.
What does a conductivity measurement mean for water?
We can use conductivity as an early warning system for potential problems that warrant further testing. If we see a variance (either lower or higher) from our baseline readings, we know something may have gone wrong. While lab testing is the usually the only way to determine what is causing the reading, higher readings could indicate a pollution event has taken place.
What about ocean water? Conductivity reading for ocean water is about 55,000 µS. While some people test conductivity in sea water, many meters won’t read that high. Many protocols choose to measure salinity instead. Salinity is measured in parts per thousand, with the average ocean reading measuring 35 ppt. Just like with all tests, we can convert readings, although conductivity measures everything that conducts electricity, while salinity only measures salt.
Some common values
|Distilled water||0.5 – 3 µS|
|Melted snow||2 – 42 µS|
|Has effects on fish reproduction||over 500 µS|
|Tap water||50 – 800 µS|
|Potable water||30 – 1500 µS|
|Freshwater streams||100 – 1,000 µS|
|Industrial wastewater||10,000 µS|
|Sea water||55,000 µS|
E.g. Most readings for the Ottawa river are below 100 µS, but near a storm sewer could have conductivity values over 2,000 µS (or 2.0mS).
Ask an expert
Conrad Gregoire, Chemist, introduces Conductivity
Water Rangers Testing Protocol
- Pull off bottom cap. It can be a bit tough, but it’s a ‘pull’!
- Turn on the meter by pressing the top button.
- Dip meter into the water. Do not dunk the whole device in as the battery is near the top. Hold in the water for 2 minutes, swishing it around lightly. Continue until both values remain steady for 30 seconds.
- Press the ‘hold’ button (middle button). (tip: If you get a reading of 10 or less, you have not removed the cap or you have taken the sensor out of the water before reading)
- Pull up meter and read the measurements. We record in µS/cm (microsiemens per centimetre), so check the units. If you get a reading like1.3, it is converting it to mS (millisiemens) and you must multiply 1.3 by 1000 and record 1,300 in your form.
- Make sure you turn off the device after use to preserve battery life (top button).
How to test for conductivity
Taking care of your conductivity meter
Since the probe is conducting an electric current, it is so important to keep the electrode clean. Rinse electrode in distilled water often, and especially if you are taking samples where readings are high or if the area is polluted.
Ask an expert
Conrad Gregoire, Chemist, how to test and use a reference to make sure you’re accurate.
Get started with testing conductivity here:
Contributing to the community!
Water Rangers is citizen-scientist led. So, if you have any questions, ideas, or notice any errors, please tell us!
We are currently conducting research involving tests for high level phosphates, but have yet to find tests that we’re happy with. Field tests that are currently available on the market can you let you know if phosphates are present, but can’t tell you to what extent they are present. In other words, they’re not quite sensitive enough to be useful! Also, many of the field tests require you to handle reagents that can be toxic, and that makes disposal difficult, meaning they wouldn’t be safe for kids to use. We are watching this space closely, and working with partners to see if this can change.
Just like with phosphates, this is another parameter where the tests we’ve tried aren’t sensitive enough unless you’re in a pollution event. Probes we’ve seen don’t seem very sensitive, and experts we’ve worked with aren’t sure how accurate they are.
While we have seen some field tests that give you an ‘absence/presence’ for E. coli, they are bulky and expensive, and often single use. They also don’t give us a numerical value, making them irrelevant for natural water systems (where a count of 200 would still be safe for swimming). Absence/presence would give too many false alarms. All of this to say- you need a lab to test for E. coli!