Determination of Conductivity/Salinity/TDS in Water Sample by Using
Conductivity Meter
Objectives
Objectives of this lab includes:
To get knowledge of Conductivity/Salinity/TDS in water
To learn about the role of Conductivity/Salinity/TDS in water quality
To understand the precautions and procedures involved in the determination of
Conductivity/Salinity/TDS in water
Determination of Conductivity
Conductivity
Conductivity is the ability of ions in a solution to carry electrical current and is the reciprocal of
the solution resistivity. In water solution it is the measure of water capability to which extent it
conducts electricity.
Electric current is carried by inorganic dissolved solids (e.g., chloride, nitrate, sulfate and
phosphate anions) and cations (e.g., sodium, calcium, magnesium, iron and aluminum).
The SI unit of conductivity is S/m and milli-Siemens per meter (mS/meter). But Often
encountered in industry is the traditional unit of μS/cm. 106 μS/cm = 103 mS/cm = 1 S/cm.
It is the reciprocal of the ohm in the resistance meter.
Conductivity = 1/ resistance
Factors affecting conductivity
Factors affecting the conductivity are:
1. Number of ions present in water
2. Temperature related to dissociation of molecules into ions.
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Typical conductivities
For drinking water: 0.05 – 0.005 S/m.
For sea water: 5 S/m.
If TDS are greater than 1000mg/l, then conductivity is 2000 S/m.
Environmental significance of conductivity
Salinity
Conductivity and salinity have a strong correlation. As conductivity is easier to measure,
it is used in algorithms estimating salinity and TDS, both of which affect water quality
and aquatic life. The effect of salinity on the solubility of dissolved gases is due to
Henry’s Law; the constant used will changes based on salt ion concentrations.
Irrigation of water in ground
High salts concentration effects the irrigation of water in the ground which ultimately
affect the plants which taking that water because salts make a layer on the surface salts
will not go through that layer deposits on that layer and plants cannot have the salts and,
in that way, they will have not had good growth.
Reduction in DO (dissolve oxygen demand)
Salinity is important in particular as it affects dissolved oxygen solubility. The higher the
salinity level, the lower the dissolved oxygen concentration. Oxygen is about 20% less
soluble in seawater than in freshwater at the same temperature. This means that, on
average, seawater has a lower dissolved oxygen concentration than freshwater sources.
Conductivity Change Can Indicate Pollution
A sudden increase or decrease in conductivity in a body of water can indicate pollution.
Agricultural runoff or a sewage leak will increase conductivity due to the additional
chloride, phosphate and nitrate ions. An oil spill or addition of other organic compounds
would decrease conductivity as these elements do not break down into ions. In both
cases, the additional dissolved solids will have a negative impact on water quality.
NEQS Guidelines
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There are no standards given by the NEQS but its value is used for measure of total dissolve
solids (TDS).
Conductivity Measurement
An electrical conductivity meter (EC meter) measures the electrical
conductivity in a solution. It is commonly used in hydroponics,
aquaculture and freshwater systems to monitor the amount of nutrients,
salts or impurities in the water.
Conductivity meter
Collection, Sampling and Storage
Container: Container type should be plastic.
Sampling: Sample should be observed immediately after collection of sample but it can
be stored at degrees Celsius in the refrigerator.
Holding Time: The holding time for this sample is 28 days.
Interferences
Temperature factor is responsible for causing interference during conductivity
measurement. So, you should consider when shopping for a conductivity meter is
temperature. Many meters feature automatic temperature compensation to ensure that the
measurement is consistent over a range of temperatures.
When your sample is too far off from room temperature (25°C/77°F) the conductivity
reading will be different. This is because as the temperature increases, the ions in the
solution move faster.
To make sure that you don’t accidentally change the conductivity in your sample,
prime your probe with a "rinse sample" before testing. This relates to the last problem
regarding calibration solutions and how they can be affected when contaminated; the
same goes for your sample, especially if it has a low conductivity.
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Material required
Conductivity meter
Beaker
Water sample
Distilled water
Procedure
Calibrate the conductivity meter with distilled water to attain proper readings
Remove the protective cap, switch the meter on and insert the probe into the water
sample up to the immersion level.
Move the probe up and down or tap it to remove air bubbles from around the electrodes.
Allow the probe to reach the temperature of the water before taking a reading.
wait about 30 seconds before taking the reading. If the water is much colder than the
probe, allow a longer period, say two minutes before taking a reading.
If the meter has no temperature compensation mechanism, take the temperature of the
sample and use a correction table to get the right value.
Read the display, and record the result.
Observations and calculations
Conductivity is measured by a meter and it shows the value in micro-Siemens. If the value is
greater than 2000 then we take the value in milli-siemens.
The value is taken at room temperature. And the value of the conductivity for the given sample is
661 µS/m.
Results
The value of conductivity of the given water sample is 661 µS/m.
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Determination of Salinity
Salinity
Salinity is the measure of all the salts dissolved in water. Salinity is usually measured in parts per
thousand or parts per million (ppt or ppm).
The salt in the ocean is mostly made up of the elements
sodium (Na) and chlorine (Cl). Together they account for
85.7% of the dissolved salt. The other major components of
seawater are magnesium (Mg), calcium (Ca), potassium (K)
and sulfate (SO4). Together with chlorine and sodium they
make up 99.4% of the salt in the ocean.
The average ocean salinity is 35ppt and the average river
water salinity is 0.5ppt or less. This means that in every
kilogram (1000 grams) of seawater, 35 grams are salt.
Environmental Significance
Salinity is an ecological factor of considerable importance, influencing the types of organisms
that live in a body of water. As well, salinity influences the kinds of plants that will grow either
in a water body, or on land fed by a water (or by a groundwater).
A plant adapted to saline conditions is called a halophyte. A halophyte which is tolerant
to residual sodium carbonate salinity are called glasswort or saltwort or barilla plants.
Organisms (mostly bacteria) that can live in very salty conditions are classified as extremophiles,
or halophiles specifically. An organism that can withstand a wide range of salinities
is euryhaline.
The degree of salinity in oceans is a driver of the world's ocean circulation, where density
changes due to both salinity changes and temperature changes at the surface of the ocean
produce changes in buoyancy, which cause the sinking and rising of water masses.
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Changes in the salinity of the oceans are thought to contribute to global changes in carbon
dioxide as more saline waters are less soluble to carbon dioxide. In addition, during glacial
periods, the hydrography is such that a possible cause of reduced circulation is the production of
stratified oceans. In such cases, it is more difficult to sub duct water through the thermohaline
circulation.
NEQS Guidelines
There are no hard and fast rule for salinity of water but it is related to the amount of total
dissolve solids in the water.
Collection, Sampling, and Storage
Container: Container type should be plastic.
Sampling: Sample should be observed immediately after collection of sample but it can
be stored at degrees Celsius in the refrigerator.
Holding Time: The holding time for this sample is 28 days.
Materials Required
Conductivity meter
Water sample
Distilled water
Procedure
Calibrate the conductivity meter with distilled water to attain proper readings
Remove the protective cap, switch the meter on and insert the probe into the water
sample up to the immersion level.
Move the probe up and down or tap it to remove air bubbles from around the electrodes.
Allow the probe to reach the temperature of the water before taking a reading.
wait about 30 seconds before taking the reading. If the water is much colder than the
probe, allow a longer period, say two minutes before taking a reading.
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If the meter has no temperature compensation mechanism, take the temperature of the
sample and use a correction table to get the right value.
Read the display, and record the result.
Observation
Conductivity meter showed the reading of 301 mg/L level at 250C
Results
The salinity of given water sample is 301mg/L.
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Determination of TDS
Total Dissolve Solids
Despite that we are determining the TDS with conductivity meter, the actual definition of total
dissolve solids is:
“The material which is passed through the filter paper of pore size 2 micrometer and remained
after subsequent drying in an oven at 180 degrees Celsius.”
Environmental Significance/Impacts
Temperature and TDS
As water temperature increases, the conductivity of water also increases; where TDS in
water is directly related to conductivity. For each 1°C increment, conductivity rise by 2–
4%. Temperature influences conductivity by increasing ions mobility and additionally the
dissolvability of many salts and minerals.
Taste of water
TDS concentration has a direct impact on the taste of water. A very low concentration of
TDS produces undesirable taste of water, as many people buy mineral water, which has
natural levels of dissolved solids. Increased concentrations of dissolved solids can also
have technical effects.
NEQS Guidelines
The guidelines of total dissolve solids (TDS) given for drinking and waste water are:
Waste water
For waste water total dissolve solids should be less than 3500 mg/
Drinking water
TDS should be less than 1000 mg/l.
Collection and Sampling
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Container: For collection of sample use clean glass or plastic bottles.
Storage: Analyze the sample as soon possible after collection but it can be stored at 4
degrees Celsius in refrigerator.
Holding Time: Sample can be stored for 7 days after collection.
Interference
There are no very prominent interferences in the water sample for solid measurement.
Materials Required
Conductivity meter
Water sample
Distilled water
Procedure
Calibrate the conductivity meter with distilled water to attain proper readings
Remove the protective cap, switch the meter on and insert the probe into the water
sample up to the immersion level.
Move the probe up and down or tap it to remove air bubbles from around the electrodes.
Allow the probe to reach the temperature of the water before taking a reading.
wait about 30 seconds before taking the reading. If the water is much colder than the
probe, allow a longer period, say two minutes before taking a reading.
If the meter has no temperature compensation mechanism, take the temperature of the
sample and use a correction table to get the right value.
Read the display, and record the result.
Observation
Conductivity meter showed the reading of 46.2 mg/L level at 250C
Results
The salinity of given water sample is 46.2 mg/L
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Comments
We have performed the above experiments to find the values of TDS/Salinity/Conductivity in the
water sample. We have used tab water as water sample to check these parameters in it. As TDS,
Salinity, and conductivity are related to each other so, the values of TDS, Salinity and
conductivity is very important in measuring of water quality specifically in oceans. We have use
the conductivity/salinity/TDS meter in the lab to measure the these parameters. It was a quite
interesting activity to perform.
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