How to Test Water Salinity

For industries such as aquaculture, agriculture, wastewater treatment, and ecological research, determining the salinity of water provides an understanding of the amount of dissolved salts and minerals in the water, which plays an important role in developing each industry. The salinity of water also determines the amount of dissolved oxygen in the water. When salinity increases, the solubility of oxygen decreases. For many aquatic organisms, dissolved oxygen is necessary for survival. Oxygen in seawater is about 20 percent less soluble than oxygen in freshwater. Salinity testing, conductivity testing, and many other methods can be used to obtain accurate measurements. This paper takes a closer look at the equipment needed to measure salinity and the importance of the measurement.

Benefits of Testing Water Salinity

There are many benefits to testing the salinity of your water. However, the exact benefits depend on the industry you are working in.

1. Ecological balance studies: Monitoring the salinity of a body of water helps to understand the health of the water ecosystem, which is beneficial for the protection and maintenance of aquatic biodiversity and the ecological balance.

2. Water quality protection: monitoring the salinity of water bodies can help identify potential water pollution problems and take appropriate measures to protect water resources.

3. Agriculture: By monitoring irrigation water salinity, farmers can choose suitable irrigation water sources and avoid the adverse effects of high salinity water on soil and crops.

4. Aquaculture: Different species of fish and other aquatic organisms have different levels of tolerance to water salinity. Monitoring the salinity of water bodies can help fisheries managers select suitable aquaculture waters and fish species and promote the sustainable development of fisheries production.

5. Industrial production: Water salinity may be an important operational parameter in some industrial processes. Understanding water salinity can help industrial enterprises to optimize production processes and improve production efficiency and product quality.

6. Human health: High salinity water may negatively impact human health, for example, by causing high blood pressure or other health problems. Monitoring the salinity of drinking water helps to ensure that the water meets health standards and safeguards human health.

Why you should use a salinity tester

One of the effective ways to measure salinity is to use a salinity tester, which will automatically provide you with a salinity reading. While conductivity sensors can help you get salinity measurements, they do not provide accurate readings.

A salinity tester can measure wastewater, surface water, and groundwater salinity. Salinometers are great for small-scale testing.

How to test water salinity

Salinity is an important parameter for measuring water quality because different livestock, crops and aquatic organisms require different salinity levels to survive. Small fluctuations in salinity can cause problems such as stress and even be fatal to living organisms, which can devastate the surrounding ecosystem.

You can use various devices to measure salinity, but maintaining the correct salinity level depends greatly on your specific use. A few common methods of salinity measurement are described next:

Handheld Refractometer

This is an inexpensive method of measuring water salinity for non-laboratory purposes. The salinity of water can be determined by measuring the change in refractive index in the water. The more salt (and other substances) dissolved in the water, the more resistance light encounters and the more it bends. This method is commonly used to test the salinity of seawater or aquarium water.

Fresh water has a salinity of less than 0.5 parts per thousand (ppt), while salt water has a salinity of about 35 ppt.

How to use it?

First calibrate to get an accurate reading.

Open the plate near the tilted end of the refractometer to expose the prism.

Please add a few drops of the sample solution with a pipette to the exposed prism.

Add a few drops of the solution to be measured to the prism.

Carefully close the plate.

To view the salinity reading, read the salinity value through the rounded end of the meter. The salinity scale may be labeled 0/00, meaning "parts per thousand," and ranges from 0 to 50.

Wipe the prism with a soft, damp cloth until there are no water droplets.

Specific Gravity Meter

This is a cheaper tool for measuring water salinity and relies on Archimedes' principle to measure the specific gravity of water. That is, the upward force exerted on an object partially or completely submerged in a fluid equals the weight of the discharged liquid. This method cannot be used for solid materials like soil salinity.

If you use a liquid hydrometer, calibrate it by noting the temperature on time to calculate an accurate salinity reading. It is recommended that the hydrometer be calibrated to 60 °F (16 °C) or 77 °F (25 °C), as these are the general standards for testing the salinity of water.

There are two types of hydrometers: glass hydrometers and pendulum hydrometers. Glass hydrometers that float in water are generally more accurate than other designs but usually do not list the exact measurements (longer decimals). Plastic "swing-arm" hydrometers may be cheaper and more robust but tend to become less accurate over time.

How to use it?

1. Remove the water sample and place it in a container. Ensure you put in enough water so the hydrometer can be immersed deep enough.

2. Measure the temperature of the water being measured.

3. Clean the hydrometer with fresh water.

4. Place the hydrometer into the sample. Note that the glass hydrometer will float. This is normal.

5. If air bubbles are on the hydrometer, gently shake them until they disappear. 6.

6. If using a swinging arm hydrometer while keeping it horizontal, take a reading pointing to the water sample's specific gravity. 7. if using a glass hydrometer, take a reading pointing to the specific gravity of the water sample.

7. If using a glass hydrometer, the measurement will be taken where the water's surface touches the meter - make sure that the measurement is taken on a flat surface of the water and not on a curved liquid surface.

8. If desired, convert the relative specific gravity (sg) to salinity.

Conductivity Meters

Instead of providing a direct salinity reading, a conductivity meter measures the electrical conductivity of water. A conductivity meter or EC meter is the only commonly used device to measure soil salinity. It can also measure water salinity, but a high-quality EC meter can be much more expensive than a refractometer or hydrometer.

There are usually two types of conductivity probes: conventional conductivity probes and those used in industrial industries. The advantage of EC probes is that they can measure not only the salt content of the water but also the nutrients and impurities in the water, covering a much more comprehensive range of industries, such as aquaculture and hydroponics.

How to use it?

Calibrating the liquid temperature

If testing for salinity in soil, mix soil 1:5 with distilled water.

Remove the protective cover from the EC sensor.

Immerse the EC probe in the sample to the desired level.

Move the probe up and down to remove air bubbles.

Adjust the temperature, some EC meters adjust automatically which may give you inaccurate readings.

Read the result from the display. Measurements may be given in mS/cm, dS/m or mmhos/cm. Fortunately, these 3 units are equal in size, so you do not need to convert between them.

Salinometers

Salinometers are electronic devices specifically designed to measure salinity. They use specially designed sensors and measurement techniques to provide fast, accurate, reliable salinity measurements. Convenient and widely applicable, they can be used in a variety of water types, including freshwater and seawater, to meet the needs of different industries and sectors.

How to use it?

Calibrate the salinometer as required.

Prepare a sample of the water to be measured, ensuring it is clean enough and free from impurities that could affect the results.

Place the water sample in the measurement tank or the salinometer chamber, ensuring that the sample covers the sensor or probe.

Start the salinometer.

Wait a certain amount of time until the salinometer completes the measurement.

Record or save the measurement results for data processing or further analysis as required.

After the measurement is complete, clean the salinometer to avoid the effect of water sample residue on the next measurement.

Why is it important to test the salinity of water

Ecological Protection

Water salinity is one of the key factors in the survival of aquatic organisms. Testing salinity is critical for surface water and aquaculture because different species of organisms have different tolerance ranges for salinity. By testing the salinity of water, it is possible to understand the ecosystem health of a water body and to protect and maintain the diversity and ecological balance of aquatic organisms.

Groundwater Resources

Salinity testing is one of the most important indicators for assessing groundwater quality. Measuring the salinity of groundwater gives an indication of the salt content of the topsoil. By testing the salinity level in the soil, you can see how much salt is extracted by plant roots. Testing soil salinity levels is usually done after the irrigation season when salinity levels are highest.

Agricultural irrigation

Water salinity is critical to agricultural production. Measuring water salinity in agriculture ensures the safety and cleanliness of irrigation water and drinking water for livestock. Excessive salinity can affect soil quality, crop growth and yields. Testing the salinity of irrigation water can help farmers choose the right source of irrigation water to avoid soil salinity problems and improve crop yield and quality.

Drinking water

Drinking water with a high salinity level may have negative effects on human health, such as high blood pressure. Therefore, testing the salinity of drinking water is essential to safeguard human health.

Industrial Wastewater

In industrial wastewater treatment, salinity testing is critical to first confirm the salt content of the water before it is re-discharged into the surrounding environment. Salt typically enters wastewater systems through agricultural, sewage and stormwater runoff. Measuring salinity is therefore vital to monitor small changes in salinity levels and take timely action to prevent adverse effects on plants, animals and the environment.

Salinity is the amount of dissolved salts and minerals in a body of water. The effects of salinity can be found in any body of water. Aquatic organisms that live in freshwater require small amounts of dissolved salts to survive. On the other hand, saltwater organisms cannot survive in water with low salinity.

Water salinity affects the environment, ecosystems, agriculture, human health and economic activities. In the natural environment, salinity directly affects the survival and distribution of aquatic organisms, and high salinity waters may lead to biodiversity reduction and ecosystem destruction. In agriculture, using high-salinity water sources for irrigation may lead to soil salinization, affecting crop growth and yields. In addition, salinity impacts human health, and excessively saline water may have negative health effects. In summary, changes in salinity have a significant impact on the natural environment, human society and economic activities, and their monitoring and management are therefore essential.

Water Salinity Testing Summary

Salinity is an important water parameter that has been tested in different industries. By measuring the salinity of water, we can understand the chemical composition of a body of water to assess its suitability and impact. This test is critical for several fields. Regular water salinity testing through equipment such as refractometers, hydrometers and salinometers allows us to keep abreast of changes in water quality. Appropriate measures are taken to protect water resources, maintain ecological balance and promote sustainable development.