The salinity of drinking water is an important indicator of its quality. This aspect is particularly relevant in hot, dry, and coastal regions where water resources are vulnerable to marine intrusion. Elevated salinity not only alters the taste and odor of water, but if persistent, can also affect human health and the water supply. Therefore, it is crucial for citizens, hydraulic engineers, and water resource managers to understand the parameters and control strategies for drinking water salinity.
Determination of water salt content
The salinity of water is determined by the amount of dissolved salts and minerals. The main compounds that affect the salinity of water are sodium (Na⁺) and chlorine (Cl⁻). Technical assessments often use a metric called “Total Dissolved Solids” (TDS). TDS is measured in milligrams per liter (mg/L) and indicates the total amount of dissolved salts in the water.
In total:
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Freshwater: less than 1000 mg/L
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Saline solution: 1000 to 3000 mg/l
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Salt water: more than 3000 mg/l
The higher the TDS value, the saltier the water tastes and the worse the drinking water quality.
The importance of monitoring the salinity of drinking water
Controlling water salinity is important for several reasons:
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Human health:
Sodium-rich drinking water can be harmful to people with cardiovascular disease, kidney disease, or high blood pressure . For people on a low-salt diet, excessive sodium intake through water is extremely dangerous. -
Consumer acceptance:
Water with high salt content tastes unpleasant, and consumers are often reluctant to drink it. In this case, people may resort to bottled water or other sources, leading to higher living costs. -
Corrosion of appliances:
High salt levels in water can increase corrosion of pipes, water tanks, and appliances such as refrigerators and washing machines. This shortens the lifespan of the water supply system and increases maintenance costs. -
Water management:
In areas with limited water resources, increased salinity can reduce the effectiveness of treatment and water supply systems and increase the need for more expensive methods such as desalination.
International standards for the salinity of drinking water
1. World Health Organization (WHO) standards
The World Health Organization (WHO) focuses on the salinity of drinking water, not on its toxicity or harmfulness. The organization recommends that the chloride concentration in drinking water should not exceed 250 mg/l and the sodium concentration should not exceed 200 mg/l. However, in hot and dry regions or areas with limited freshwater resources, higher salinity levels may be temporarily acceptable, provided their health effects are monitored.
2. Other national standards
In many countries, such as the USA, the permissible total dissolved solids (TDS) in drinking water is 500 mg/L. For people on a low-salt diet, 250 mg/L of chloride and approximately 20 mg/L of sodium are recommended. In Australia, water with a TDS value below 600 mg/L is considered high-quality, water between 600 and 900 mg /L is considered average, and water above 900 mg/L is considered poor.
The health effects of water with high salinity
Water with high salinity can have the following effects on human health:
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Excessive sodium consumption: Can lead to high blood pressure and worsen heart and kidney disease.
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Gastrointestinal irritation: Some people may experience stomach upset after drinking salt water.
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Taste changes and reduced water intake: Salty taste can cause people to drink less water, which can increase the risk of dehydration in hot, dry regions.
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Indirect effects: When people drink sugary drinks or bottled water because they don’t like the taste, they are at increased risk of obesity and diabetes.
Therefore, maintaining an acceptable salt level is crucial not only for health but also for improving the quality of life.
Salinity of drinking water in Iran
Salinity poses a serious problem for drinking water supplies in Iran, especially in the southern, eastern, and central regions. The main factors contributing to rising salinity include insufficient rainfall, overexploitation of groundwater, and the intrusion of seawater into aquifers.
In some coastal cities such as Bushehr, Bandar Abbas, and Chabahar, the total dissolved solids (TDS) content of natural water sources can exceed permissible levels. In these cases, water treatment and desalination are often used to reduce salinity. Groundwater salinity has also increased in inland cities due to increased evaporation and soil drying .
The National Organization for Standardization of Iran (NISA) has set the permissible limit for total dissolved solids (TDS) in drinking water (Standard No. 1053) at 1000 mg/L. It also sets the permissible limit for sodium at 200 mg/L and for chloride at 250 mg/L. These values are in line with international standards and aim to ensure the quality and safety of drinking water in various regions of Iran.
Methods for reducing the salinity of water
1. Choose a low-salinity water source: When planning
your water supply, choose a low-salinity source. Surface water sources such as rivers or reservoirs are generally less saline than groundwater.
2. Desalination and purification:
If the water has high salinity, technologies such as reverse osmosis (RO), distillation, or ion exchange can be used. RO is one of the most effective methods for reducing total dissolved solids (TDS) and is currently used in many cities in southern China.
3. Mixing brackish and fresh water:
In areas with water sources of different salinities, the final salinity can be adjusted to the desired level by controlling the water mixture.
4. Continuous monitoring and control: By regularly monitoring water quality and recording dissolved solids , sodium and chloride
levels, changes can be detected early and crises can be prevented.
5. Prevention of seawater intrusion:
In coastal areas, the construction of groundwater dams, controlled water abstraction from wells and groundwater recharge can prevent the intrusion of seawater into freshwater sources.
6. Public awareness: Public awareness of water quality
and salinity control measures can increase public confidence and cooperation in efficient water use.
Summary and conclusion
The salinity of drinking water is an important factor in its quality and health. Although it generally does not cause toxicity, it can directly impact water taste, heart and kidney health, and even consumer behavior.
The globally recommended values for sodium are 200 mg/l, for chlorides 250 mg/l, and for dissolved solids 500 to 1000 mg/l. In Iran, these values have been adopted as official standards.
To control the salinity of drinking water, various technical and administrative measures must be implemented , such as the selection of appropriate water sources, water purification and desalination, continuous monitoring, and public awareness.
Adherence to these principles ensures the provision of safe, high-quality water, mitigates the health and economic impacts of high salinity, and effectively promotes the sustainable use of the country’s water resources.