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Quality Characteristics That Drinking Water Should Have

Although humanity has come a long way on the path to civilization, one of the biggest problems of the world today is the inability of the entire population to access potable water.

About 32% (2.5 billion) of the world’s population is currently deprived of clean drinking water. As a result, deaths and serious health problems occur. The water hardness is also very important in terms of usage, even if it is not for health.

For water to be drinkable, it must have certain characteristics and a certain quality. The sensory appearance of the water as clean and clear may evoke the perception that water is drinkable.

However, at its simplest, seawater, however clean and clear it may appear, is not drinkable. Therefore, measuring potable water quality is possible not only by appearance but by testing many other criteria.

The World Health Organization (WHO), the European Union (EC) and the US Environmental Protection Agency (EPA) define the quality criteria that drinking water should have; In Turkiye, it is determined by the Turkish Standards Institute (TSE) and the Public Health Institution of Turkiye.

Although it is evaluated under different topics by different institutions, it would be more reasonable to evaluate the quality criteria of drinking water under 4 headings.

1. Sensory Criteria of Water

The first condition for drinkable water is that it has good sensory properties. What is meant by sensory characteristics are color, smell, taste and clarity of the water. The water should be colorless and odorless.

If water has any color or smells water that means it contains metal ions or a significant amount of microorganisms. The water should have a distinctive flavor; It should not taste bitter, salty or sour.

Likewise, the water should not be cloudy. Turbidity in water is caused by particles suspended in the water. These particles can be clay, microorganisms, organic or inorganic substances.

For whatever reason, cloudy water is not drinkable. Turbidity can be detected both visually and instrumentally and it has certain limits as stated below.

Sensory criteria are an important way to understand whether water is potable without any instrumental analysis; however, it is not sufficient on its own to make a decision.

Sensory criteria prevent the use of waters that do not have as appropriate sensory properties as drinking water, but waters with appropriate sensory properties must also be evaluated by other criteria.

2. Physical and Chemical Criteria of Water

pH of Water

pH is the parameter that shows whether the water is acidic or basic. Water above pH 7.0 is basic, while those below 7.0 are acidic. Pure water has a pH of 7 and is therefore neutral.

The presence of minerals (dissolution of ions) in the water changes the pH and character of the water. By nature, water is either acidic or basic, depending on the types and amounts of dissolved ions.

In general, the pH of healthy drinking water is between 6.5 and 9.5. However, it is desirable that the water be somewhat basic. Because acidic water, especially below pH 6.5, is corrosive and acidic water corrodes transport pipes and thus metal ions mix with the water.

Another aspect of pH in drinking water is that it is a measure of the richness of the minerals it contains. The increase in the basicity of the water (depending on the composition of the minerals it contains), provided that the pH is 9.5 is the limit, can be used as an indicator that the drinking water is of higher quality and nutritive.

If the water has a pH higher than 9.5, it causes a worsening of the taste and a slippery feeling. On the other hand, pH outside the 6.5-9.5 limits indicates pollution.

Water Hardness

By definition, water hardness is the amount of ions with 2 or more valences (Mg+2, Ca+2) in mmol/liter water. In other words, water hardness refers to the amount of salts dissolved in the water, formed by calcium and magnesium combined with carbonate (CO3), bicarbonate (HCO3) and sulfate (SO4). These salts pass into the water through soil and rocks in their underground route.

In general, the hardness caused by carbonate and bicarbonate salts of calcium and magnesium (CaCO3, MgCO3, Ca(HCO3)2, and Mg(HCO3)2) is called “temporary hardness”, and the hardness caused by sulfate salts (CaSO4 and MgSO4) is called “permanent hardness”. The sum of temporary and permanent hardness is expressed as “total hardness”.

The reason why is called temporary hardness to hardness caused by the carbonate and bicarbonate salts of calcium and magnesium is the hardness can be removed by boiling the water or adding slaked lime (CaOH – calcium hydroxide) to the water. Lime formation in teapots is the most well-known example of removing temporary hardness.

Permanent hardness cannot be removed by heating the water or adding slaked lime to the water. However, permanent hardness is also removed. Na2CO3 is added to the water to remove permanent hardness.

Currently, the consensus within the scientific community is that hard water is not harmful to health. The World Health Organization (WHO) declared at the Geneva Conference that hard water has no known adverse health effects.

Moreover, some researchers argue that hard water is a rich source of calcium and magnesium. In fact, there are scientific studies that report that hard water is good for cardiovascular diseases and some types of cancer.

On the other hand, some studies show that hard water has no or very low effect on kidney stone formation. As a result, the data on the possible effects of water hardness on health is not sufficient for now and studies and discussions in this direction continue at full speed.

Therefore, there is currently insufficient data to recommend a minimum or maximum mineral concentration for health related to water hardness and therefore no guideline values ​​are recommended.

Researcher Sengupta’s review titled “Potential Health Impacts of Hard Water” published in the International Journal of Preventive Medicine stands out as a very useful and must-see study in terms of summarizing the point reached by scientific studies on this subject.

Different units are used to measure the hardness of the water. These units are;

French Degree of Hardness -1of = 10 mg CaCO3/liter 8,4 mg MgCO3/liter

British Degree of Hardness – 1oe = 14,3 mg CaCO3/liter 2,0 mg MgCO3/liter

German Degree of Hardness – 1odH = 10 mg CaCO3/liter 7,1 mg MgCO3/liter

American Hardness = 50 mg CaCO3/liter 42 mg MgCO3/liter

Classification of water hardness

Water HardnessAccording to the French degree of hardnessAccording to the German degree of hardnessAccording to the British degree of hardness
Slightly Hard14-228-1210-15
Very Hard32-5418-3022-35

In Turkiye, the French Hardness Degree is used as the hardness unit and the waters are classified accordingly. In general, it is recommended that the hardness of drinking water in Turkiye should not exceed 12 o F.

In general, in the evaluation according to the amount of ions in the water, the total concentration of Mg+2 and Ca+2 ions;

“Soft” if it is less than 0,6 mmol/liter,

“Slightly hard” if it is between 0,6-1,2 mmol/liter,

“Hard” if it is between 1,2-1,8 mmol/liter,

• More than 1,8 mmol/liter is classified as “very hard”.

Another classification in terms of quantity is as follows;

“Soft” if there is calcium carbonate (CaCO3) between 0-60 mg/liter in the water,

“Partly hard” if calcium carbonate (CaCO3) is between 61-120 mg/liter,

• If there is calcium carbonate (CaCO3) between 121-180 mg/liter, it is classified as “hard”.

If the amount of calcium carbonate (CaCO3) in the water is more than 100 mg/liter, corrosion and scale formation; If it is more than 500 mg/liter, taste and flavor problems occur in meals and beverages.

Although there are discussions about the effects of water hardness on health, it can be said that the use of hard water in cleaning causes problems such as skin dryness, hair loss and dandruff formation in the hair.

On the other hand, as a result of the use of hard water other than drinking water, if hard water is used in food and beverage production, it causes undesirable taste formation, hardening of vegetables and delayed cooking.

The use of hard water in cleaning causes foam cuts and shortens the life of the washed clothes. Hard water causes calcification in the dishwasher, washing machines, sanitary water system and heating system.


Measuring the conductivity of water is another way to determine the amount of ions dissolved in the water. As mentioned earlier, pure water is neutral and does not conduct electricity.

As the amount of ions dissolved in water increases, the conductivity naturally increases. Therefore, if the amount of conductivity is measured, the amount of pollution in the water will also be measured. The conductivity of drinking water should be a maximum of 2500 µS/cm at 20oC.


Sensorially observable turbidity was mentioned above. Turbidity can be caused by inorganic and organic substances, microorganisms and particles such as clay suspended in the water.

Instrumentally, the turbidity of the water should be a maximum of 5-25 NTU (nephelometric turbidity units) (some accept standard 5 NTU, some accept 25 NTU as standard).

Pesticide Residue

Pesticides are chemicals used in agriculture to combat agricultural pests. They may be mixed with drinking water during underground activities.

Because of the serious health hazards of pesticides, it is extremely important to monitor their possible admixture into drinking water.

The term pesticide includes insecticides, herbicides, fungicides, nematocides, acaricides, algaecides, rodenticides and their associated products (growth controllers, among others) and their associated metabolites, degradation or reaction products.

In the Ministry of Health’s Water Intended for Human Consumption Regulation, the highest amount of pesticide allowed in drinking water is 0,10 µg/liter. Among these, the limit value for aldrin, dieldrin, heptachlor and heptachlor epoxide is 0,030 µg/liter. The limit value of the total pesticide amount is 0,50 µg/liter.

Other Chemical Criteria

Many different contaminants from many different vectors can be involved in drinking water. The limit values ​​for the substances in question to be found in drinking water are as follows;

MaterialLimit value (in a liter of water)
Acrylamide0,1 µg
Chloride250,0 mg
Free chlorine0,5 mg
Ammonium0,5 mg
Sulfate250,0 mg
Iron0,2 mg
Aluminum0,2 mg
Sodium200 mg
Antimony5,0 µg
Arsenic10,0 µg
Benzene1,0 µg
Benzo (a) pyrene0,010 µg
Boron1,0 mg
Bromate10,0 µg
Cadmium5,0 µg
Chromium50,0 µg
Copper2,0 mg
Manganese50,0 µg
Cyanide50,0 µg
1,2-dichloroethane3,0 µg
Epichloride0,10 µg
Fluoride1,5 mg
Lead10,0 µg
Mercury1,0 µg
Nickel20,0 µg
Nitrate50,0 mg
Nitrite0,50 mg
Polycyclic aromatic hydrocarbons (PAH)0,10 µg
Selenium10,0 µg
Tetrachlorothene and trichloroethene10,0 µg
Trihalomethanes-total100,0 µg
Vinyl chloride (VC)0,50 µg

3. Microbiological criteria

The presence of microorganisms in drinking water is an extremely risky situation for health. Naturally, controlling the presence of microorganisms in drinking water is of critical importance.

Adding chlorine to drinking water, known as “chlorination” in society, is done to kill microorganisms in the water.

In this context,

• In analyses made in 250 milliliters of drinking water, E. coli, Enterococcus, Coliform bacteria and P. aeruginosa strain bacteria,

• Sulfite-reducing bacteria with anaerobic spores in 50 milliliters,

• Pathogenic staphylococci in 100 milliliters,

• 5 liters should not contain parasites.

4. Radioactive criteria

The monitoring of radioactivity in drinking water is of critical importance not only in terms of individual and public health but also in terms of the health of generations and the functioning of nature.

In this context, Tritium in drinking water is accepted as 100 Bq/liter and the total indicator dose is 0,10 mSv/year as the limit value. According to the Turkish Standards Institute, TS 266 Drinking Water Standards, 0,037 Bq/liter for alpha activity and 0,37 Bq/liter for the beta activity of drinking water are accepted as limit values.

Here are some of the articles that might interest you;

Water and Health; Functions in the Body and Daily Needs

Water in Foods; Forms, Characteristics and Importance

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