Water is one of the most important resources for humans, agriculture, and industry. In many regions, especially in the arid and semi-arid areas of Iran, well water serves as the primary source of drinking water, irrigation, and livestock watering. However, a common problem with groundwater use is elevated salinity . Excessive salinity not only affects the taste and quality of the water but also damages soil, plants, equipment, and even human health.
This article examines the concept of salinity in water, the causes of its increase, measurement methods, and strategies for reducing it.
What is meant by the term salinity of water?
The salinity of water is determined by the amount of dissolved salts , particularly sodium, chloride, sulfate, magnesium, and calcium ions. The higher the concentration of these salts, the higher the salinity of the water. Salinity is usually expressed in millisiemens per centimeter (mS/cm) or as total dissolved solids (TDS) in milligrams per liter (mg/L) .
For better understanding, the following table shows the typical range of salinity in water:
| Water type | Total dissolved solids (mg/L) | He explains |
|---|---|---|
| Freshwater | Less than 1000 | Suitable for human consumption and agricultural use. |
| Brackish water | From 1000 to 3000 | Can be used in agriculture under certain conditions. |
| brine | From 3000 to 10000 | Not suitable for consumption and subject to restrictions for some resistant plants. |
| The water is very salty. | More than 10,000 | Not suitable for agricultural or human purposes. |
Factors that influence the salt content of well water
There are many reasons for a high salt content in groundwater. Among the most important are:
1. Geographical location
In some areas, the earth’s layers contain evaporated rocks such as salt (rock salt) or gypsum . When water flows through these layers, it dissolves some of the salt, thus increasing the salinity.
2. Lowering of the groundwater level
Overexploitation of groundwater has led to a drop in the groundwater level and the intrusion of saltwater from deeper aquifers into freshwater areas. This phenomenon occurs particularly frequently in arid regions of Iran such as Khuzestan, Sistan, and Kerman.
3. Seawater intrusion
In coastal areas, a falling groundwater level can lead to saltwater intrusion into freshwater reservoirs. This phenomenon, known as saltwater intrusion, poses one of the greatest threats to coastal waters.
4. Insufficient irrigation
The continuous use of saline irrigation water leads to an accumulation of salts in the soil, which over time seep into the groundwater and thus increase the salt content of the well water.
5. Industrial and agricultural wastewater
The introduction of wastewater, industrial wastewater, fertilizers and pesticides into the soil gradually increases the concentration of dissolved salts in the groundwater.
PureTec Reverse Osmosis: Basics
Methods for measuring the salinity of well water
There are many ways to measure the salt content of well water; the most common are:
1. Use an EC meter
Electrical conductivity (EC ) measures the amount of salt dissolved in water . The higher the salt concentration, the higher the EC. EC meters display the salt concentration digitally in microsiemens/cm² or millisiemens/cm²
.
2. Measurement of total dissolved solids
TDS stands for “Total Dissolved Solids”. Many household and industrial measuring devices for measuring TDS values are suitable for easily determining salt concentration.
The approximate relationship between conductivity and TDS value is as follows:
Total amount of dissolved solids (mg/L) ≈ EC (µS/cm) × 0.64
3. Laboratory analysis
Water samples must be analyzed in a laboratory to accurately determine the type and quantity of ions that influence salinity (e.g., chloride, sodium, magnesium, and calcium). This method is essential for the design of agricultural water treatment and wastewater treatment facilities.
The effects of water salinity on the environment and humans
Excessive salt content in well water can have various consequences:
-
In agriculture: The plants absorb less water, their leaves burn, their growth and productivity decrease , ultimately leading to soil salinization.
-
In industry: formation of deposits and corrosion on equipment and steam boilers.
-
In domestic use: Unpleasant odors develop, deposits form in the pipes, and the lifespan of appliances such as water heaters is shortened.
- Health effects on humans: Chronic use can lead to high blood pressure and kidney problems.
Methods for reducing the salt content of well water
If the water in a well has a high salt content, physical, chemical, and organizational methods can be used to reduce it:
1. Reverse osmosis filtration (RO filtration)
Reverse osmosis systems (RO systems) are among the most effective methods for removing dissolved salts. In this process, water is forced under pressure through a semipermeable membrane to separate the salts.
This method is widely used in households, greenhouses, and industry.
2. Distillation
During distillation, water evaporates and the vapor condenses. Because salt is left behind during evaporation, the resulting water is very sweet. However, a disadvantage of this method is its high energy consumption.
3. Use of ion exchange resin
In this system, sodium or calcium ions are replaced by harmless ions such as hydrogen or potassium. This method effectively reduces water hardness, but its effectiveness is limited in water with a high salt content.
4. Mix with fresh water.
If you find a less saline spring, you can reduce the salinity by combining the springs. This is a simple, but only temporary, solution.
5. Water resources and irrigation management
-
Preventing the overexploitation of oil sources
-
Proper drainage of agricultural land
-
Cultivation of salt-tolerant crops such as barley, wheat or oats.
Important tips for farmers
-
Always have well water chemically analyzed before use.
-
If the electrical conductivity of the water exceeds 3 dS/m, use drip irrigation and flush the soil regularly.
-
In saline soils, the use of agricultural gypsum (CaSO₄) can help reduce the effects of sodium.
-
If you notice a sudden increase in the salinity, check the water level in your well; this could be a sign that salt water is seeping from below.
In conclusion
The salinity of well water poses a serious challenge to groundwater management, particularly in Iran. Increasing well water withdrawals, climate change, and anthropogenic pollution are the main causes
. Regular water quality monitoring , appropriate treatment processes , and systematic water management can significantly reduce the negative effects of salinity.
Monitoring the salinity of well water not only improves agricultural production and extends the lifespan of facilities but also plays a crucial role in protecting human health and ensuring the sustainable use of water resources.