According to drinking water standards, the water must be epidemiologically safe, chemically harmless and have good organoleptic properties. Water quality depends on the content of impurities in it which are regulated by the standards set by each country. In Latvia these are Regulation No. 547 “Mandatory safety and quality requirements for drinking water, monitoring and control procedures/Dzeramā ūdens obligātās nekaitīguma un kvalitātes prasības, monitoringa un kontroles kārtība“.
In this article we will look at the most important water indicators and their permissible values. By knowing the specific properties of the water it is possible to improve water quality and solve related problems.
TASTE AND SMELL
Taste and smell are organoleptic properties of the water that can cause discomfort to humans. The smell and taste of the water is evaluated by five-point scale. 0 indicates that the water has no smell/taste, while a score of 5 indicates a very strong smell/taste of the water.
Bad smell and taste of water indirectly indicate the presence of certain pollutants such as dissolved salts, various chemical and organic compounds.
Some examples:
- salty taste may indicate excess of sodium chloride;
- bitter taste may indicate sodium or magnesium sulfates;
- tart taste can indicate iron and aluminum sulfates, as well as excess lime;
- metallic taste can indicate an excess of iron, manganese and copper;
- soapy taste may indicate sodium carbonate;
- sweet taste may indicate sodium bicarbonate;
- irritating rotting smell can indicate microorganisms in the water.
More information about the taste and smell of water is available here.
TURBIDITY
Turbidity is a reduction in the transparency of the water when it contains finely dispersed organic and inorganic impurities. The most common pollutants that cause water turbidity are sand, clay, various carbonates (water like milk), sludge formed by phytoplankton and zooplankton (yellow-green water with an unpleasant smell).
In order to find out the turbidity of the water, analysis in laboratory is usually carried out and it is expressed by turbidity units per liter of the water or so called NTU (nephelometric turbidity units). The World Health Organization has set a maximum turbidity value for drinking water that is 5 NTU. On the other hand, in Latvia Regulation No. 547 determines that the turbidity of the water must be within 0.3 -1 NTU.
More information on water turbidity is available here.
COLOR
Water color is one of the characteristics of the water quality that can be assessed visually. Although quite a number of factors can affect the color of the water, the main ones are water impurities and microorganisms living in it.
The main reason for the yellowish hue of water is iron or humic substances (humic and fulvic acids) dissolved in it. Green color in the water body describes the development of blue-green algae in it. The brown color of the water is caused by biological processes such as rotting in bogs. Relatively rarely the brown or red color is also caused by mineral salts (e.g. iron compounds). Milk-colored water, on the other hand, is formed due to dissolved oxygen in it or pollution caused by industrial wastewater.
More information about water color is available here.
OXIDABILITY
An oxidizability greater than 5.0 mg O2/l indicates a high organic matter content and may indicate possible water pollution by sewage or poor overall condition of the water source (e.g. algae, low water level, flooding, etc.). Such water is usually contaminated with microorganisms and causes the water to foam. It is not recommended to use such water in food, it needs to be purified beforehand.
DRY RESIDUE
The dry residue determines the total amount of inorganic salts of calcium, magnesium, potassium, sodium, heavy metal minerals dissolved in the water, as well as a large percentage of organic substances. This parameter is mainly used to determine the general mineralization of the water.
Its value in drinking water should not exceed 1000 mg/l. An increased content of dissolved substances in water prevents its use for steam boilers due to a decrease in their operational efficiency (increased flow rate), in certain spheres such water cannot be used in production (e.g. in the production of synthetic rubber, kapron, film and condenser paper).
HARDNESS
Water hardness is the total amount of dissolved ions of alkaline earth metals (mainly calcium and magnesium). When performing water analysis in the laboratory, the hardness is evaluated with a water hardness indicator. A value of up to 1.5 mmol/l characterizes very soft water, while a value of more than 12.0 mmol/l characterizes very hard water.
Very hard water has bitter aftertaste. Long-term consumption of such water overloads the urinary system which can lead to the formation of kidney stones, hypertension and edema. In households, hard water forms deposits on the heating elements of heating boilers and washing machines, reducing the energy efficiency of these devices. In industry, however, water hardness is strictly regulated in certain sectors. Limestone is dangerous for water heating and steam boilers, it reduces the service life of equipment and increases energy costs.
Water hardness in domestic and drinking water supply systems should not exceed 7 mg-equiv/l (in some cases up to 10 mg-equiv/l) but for certain technologies the requirements may be even more strict. For example, the hardness of the supply water of a steam boiler should not be higher than 0.02 mg-equiv/l.
More information about water hardness is available here.
HYDROGEN INDEX (PH)
The hydrogen index (pH) describes the concentration of hydrogen ions in a solution. To characterize and compare this parameter, the pH scale is used, which ranges values from 0 to 14. A pH value of 7 characterizes a neutral environment where the concentration of hydrogen ions and hydroxide ions in the solution is the same. Such an environment is characteristic of completely pure water. If the pH value is less than 7, then the environment is considered acidic, if the pH value is above 7, then the environment is considered alkaline.
The pH value of drinking tap water should be between 6.5 and 8.5. Long-term consumption of water that does not meet the mentioned requirements can cause health problems.
The pH value, along with other water quality indicators (e.g. temperature, total alkalinity, calcium content and dry residue) allows us to draw conclusions about the water’s ability to deposit calcium carbonate or cause corrosion on the metal surface.
More information about alkaline water is available here.
IRON
Iron is most common in well water as it is a natural impurity in groundwater. Due to the lack of air it does not oxidize and can reach an extremely high value. For tap water more common is secondary contamination with iron in the water pipelines when rust flakes and iron-organic compounds are washed out from the pipes.
The iron content in drinking water should not exceed 0.2 mg/l. Increased iron content in drinking water negatively affects the taste and the color of water, it can cause disturbances in the work of the gastrointestinal tract and can also develop allergic reactions. Such water in the household damages the sanitary equipment and in some cases causes the formation of iron deposits in the water pipes.
More information about iron in water is available here.
SULFATES AND CHLORIDES
Chlorides and sulfates are among the most common anions in the water. Most of these inorganic compounds are completely soluble in the water. Sulfates are salts of sulfuric acid (H2SO4). The most common salts in the water are sodium, potassium and magnesium sulfates. Chlorides, on the other hand, are salts or anions of hydrochloric acid (HCl). The most typical chloride is table salt NaCl.
The content of sulfates and chlorides in drinking water should not exceed 250 mg/l. Sulfates in the water by themselves do not mean much but their content, together with other indicators such as sodium or calcium, are making the total composition of minerals. Excessive sodium intake is associated with hypertension. In addition, this ion increases the electrical conductivity of the water and increases corrosion activity.
More information about sulfates and chlorides in water is available here and here.
FLUORIDES
Fluorine compounds in the water affect the musculoskeletal system. More than half of the fluoride consumed is deposited in the bones and teeth. The fluoride content in drinking water must be between 0.7 and 1.5 mg/l. A lack of fluorine in drinking water (less than 0.5 mg/l) is harmful, as well as its excess (more than 1.5 mg/l).
Fluorine participates in the work of the thyroid gland and the assimilation of trace elements including calcium. In the case of this element, its deficiency and excess are equally dangerous. A lack of fluoride can lead to the destruction of bone tissue, especially teeth, while an excess accumulates in the aorta and can cause it to become calcified.
More information about fluoride in water is available here.
AMMONIA, NITRATES, NITRITES
The presence of ammonia, nitrates, and nitrites may indicate contamination of a water source with domestic or industrial wastewater.
Ammonia in high concentration causes mucous membrane irritation. Nitrates and nitrites can cause gastrointestinal problems as well as affect fetal development. Similarly, an increased concentration of nitrates in the human body forms methemoglobin. Nitrate ions oxidize the hemoglobin in erythrocytes and interfere with the transport of oxygen to human tissues, thereby affecting the functioning of the nervous system and enzyme synthesis.
The maximum permissible nitrate concentration in drinking water is 50 mg/dm³, while the permissible nitrite concentration is 0.5 mg/dm³. These are values that do not cause adverse effects in the body and do not affect the offspring.
More information about nitrates in water is available here.
HYDROGEN SULPHIDE
A characteristic sign of increased content of hydrogen sulfide in the water is the unpleasant smell of rotten eggs. Despite the fact that hydrogen sulfide does not cause high toxicity to the human body, drinking such water is unpleasant and long-term drinking of such water can cause gastrointestinal diseases.
More information about hydrogen sulfide in water is available here.
MICROORGANISMS IN WATER
The total microbial count describes the presence of microorganisms in the water. For drinking water it is the number of aerobic and anaerobic bacterial colonies per 1 ml of water. It is determined by introducing a water sample into the culture medium and growing the colony for a certain period of time (from 3 days to a week). The permissible indicator for drinking water is 100 bacteria in 1 ml of water.
One of the most dangerous contaminants in the water is the microorganism Escherichia coli. Its presence indicates the water contamination with feces which is not acceptable for drinking water. The consequences of drinking such water can be acute diarrhea which is especially dangerous for small children.
More information about microorganisms in water is available here.
Read also: What does the water analysis say?
