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If some indicators in water analysis are quite understandable due to their wide popularity, such as nitrates, other indicators often cause many questions, especially if they go beyond the reference values. Today we will try to find out what are sulfates, what does sulfate increase in the water means and what are their impact on the human body.

What are sulfates?

Sulfates are salts of sulfuric acid H2SO4. The anion in this case is SO42-. The most common salts that can be found in water are sulfates of sodium, potassium and magnesium.

In the water analysis you can see the concentration of the sulfate ion. Sulfates by themselves does not say much but their content together with other indicators, for example, concentration of sodium or calcium, makes the overall picture of the mineral composition.

The norm of sulfates in drinking water

The content of the main mineral impurities in the water is regulated by the state sanitary standards. Maximum allowed concentration of sulfates in water of centralized water supply systems and bottled water are 250 mg/l. But maximum limit of sulfates in water from decentralized sources (such as wells and catchments) are 500 mg/l.

Where does sulfates come from?


The most logical source of sulfates are natural minerals through which water passes during its movement in nature.

In industry, the main sources of sulfates are:

  1. Mine waters. They are characterized by high mineralization (sulfates, chlorides, sodium, calcium and other mineral salts);
  2. Wastewater from ore-dressing and metal-smelting enterprises;
  3. Wastewater from leather, paper and textile enterprises;
  4. Traffic fumes.

Exhaust gases of thermal power plants, large industrial enterprises with boilers running on fossil fuels (such as coal or gas) and exhaust of cars are the sources of sulfur dioxide SO2, nitrogen oxide and other substances.

When mentioned substances start to interact with air and atmospheric water, a number of chemical transformations occur:

  • Oxidation of sulfur dioxide to sulfur anhydride;

2SO2 + O2 ➝ 2SO3

  • It reacts with water and form sulfuric acid;

2SO3 + H2O ➝ H2SO4

  • The processes of mutual oxidation also play a role.

NO2 + SO2 + H2O ➝ H2SO4 + NO

The result of these chemical processes is acid rain, which can contribute to the acidification of soils and water bodies.

Sulfates in water: the effect on human body


On average, a person from water consumes about 500 mg of sulfates per day. However, their main source of consumption is food, not water.

Sulfates are characterized by a bitter taste, which can be felt at a concentration of 250 – 600 mg/l of sodium, calcium and magnesium sulfates. The only danger of sulfates that has been identified so far is their laxative effect, which, depending on consumption, can manifest itself to varying degrees. This effect is at sulfates concentration of 1000-1200 mg/l but unpleasant taste of water is noted already at 500 mg/l. That is why the requirements for the quality of drinking water are set as a normative indicator.

Limiting the level of sulfates in tap water has another purpose as well — they can increase the electrical conductivity of water and thereby increase corrosion.

Removing sulfates

In industrial processes the removal of sulfates are technologically important task, since they increase corrosion, affect technological processes etc. Traditionally the main methods of sulphate removal are ion exchange and reverse osmosis.  If ultrapure water is required, electrodeionization can be used.

In households reducing the level of sulfates, as well as other mineral components, is the task of reverse osmosis filters.


Sulfates in water in concentration that do not cause an unpleasant aftertaste are not dangerous to humans. Limiting the concentration of sulfates is important in order to avoid corrosion of water pipes.

Chlorides and sulfates in water are the main components of the anionic composition, so their high content can indicate an increased content of sodium, calcium, magnesium and other cations, which can create a number of side effects.

Read also-Iron , Manganese

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