Physico-chemical indicators of drinking water

This concerns a set of basic indicators that characterise the composition of water and the content of basic cations and anions in water.

pH (water reaction)

pH is an indicator that expresses the acidity or alkalinity of water. Its value depends on the content of dissolved salts and dissolved carbon dioxide; the pH of groundwater (water from a well) depends on the geological properties of the rocks in a given place. Water or an aqueous solution has a neutral reaction at a pH value of 7, is acidic below 7 and alkaline above 7.
Decree No. 252/2004 Sb. permits a pH between 6.5 and 9.5 for drinking water. Water with a pH of 6.0-6.5 before treatment is also considered satisfactory, but the increased aggressive effect on pipes, boilers, etc. must be taken into account.

Colour

Drinking water should be colourless. Decree 252/2004 Sb. specifies that the colour of drinking water must be less than 20 mgPt/L (the colour scale intended to assess the colour of water is created from a platinum compound, for this reason the colour also applies to mg Pt).
The colour of natural water depends on the content of dissolved or undissolved substances. Totally clear water appears blue at a depth greater than 1m. The most common colouring of the source of drinking water is yellowish, which is caused either by an increased content of iron or humic substances (so-called peat water). Increased manganese content can cause greasy circles to appear on the surface of water that has been standing for a long time.

Taste

Decree 252/2004 Sb. stipulates that the taste of drinking water must be acceptable to the consumer.
Water itself is tasteless, its taste is determined by what ions and in what proportion they are dissolved in it. In general, water with a higher content of dissolved substances (so-called mineralised water) tastes better than so-called soft water.
The content of dissolved carbon dioxide in the water also has a positive effect on the taste. The pH also has an effect on the taste, e.g. water with a pH higher than 8 can have a soapy aftertaste. A higher content of sulphates or magnesium (or both) causes water to taste bitter, whereas a higher content of chlorides or sodium causes it to taste salty. A higher content of metals (iron, manganese and others) can cause a so-called metallic taste, etc.

Odour

Decree 252/2004 Sb. stipulates that the odour of drinking water must be acceptable to the consumer.
Water itself is odourless. The odour of water is caused by volatile substances that are dissolved in the water and are gradually released from it. The most common source of odour in natural unpolluted waters is hydrogen sulphide, which smells like rotten eggs. In water with faecal pollution, the corresponding smell of urine, liquid manure, faeces, etc. can also appear. The smell of chlorine is also common in drinking water treated on the basis of chlorination.

Water turbidity

Turbidity (reduction of water transparency) is a summary indicator of the content of undissolved and colloidally dissolved inorganic and organic substances in water (sand, oxides of iron, manganese, clay). In Decree 252/2004 Sb., a maximum turbidity value of 5 ZF is permitted for drinking water (turbidity 3 What do the drinking water parameters mean refers to the so-called formazin units).

Conductivity

An indicator that is proportional to the amount of dissolved inorganic substances (salts) in water.
In Decree 252/2004 Sb., a maximum conductivity of 125 mS/m is permitted for drinking water. The optimal conductivity range for drinking water is 25-50 mS/m.
Water with a conductivity higher than this limit (so-called mineral water) is not suitable for long-term use and can cause health problems. However, even so-called soft water without dissolved salts or with a very low salt content (water in mountain areas, rainwater, demineralised water) is not suitable for long-term drinking, as the necessary minerals are washed out of the body.

Ammonium ions (NH⁴⁺)

An increased content of ammonium ions is an indicator of possible seepage of faecal pollution (liquid manure, cesspools, wastewater) or pollution with inorganic nitrogen fertilisers. In Decree 252/2004 Sb., a maximum concentration of ammonium ions of 0.5 mg/L is permitted for drinking water.

Chemical oxygen demand (COD_Mn)

CODMn is a summary indicator, proportional to the content of organic substances dissolved in water. These organic substances can be of plant or animal origin. Very often, an increased COD value also indicates bacterial pollution. An increase in the indicator is also possible if seepage of industrial pollution has occurred. It is usually accompanied by bacterial contamination. In Decree 252/2004 Sb., a maximum concentration of COD_Mn of 3 mg/L is permitted for drinking water.

Iron (Fe²⁺ or Fe³⁺).

The increased content of iron in the source of drinking water (well) is of natural origin, i.e. the source is the rocks from which the water springs to the surface. The source can also be iron from pipes or appliances through which water flows if corrosion occurs. Iron is mostly found dissolved in water in divalent form (Fe²⁺). However, upon contact with atmospheric oxygen it oxidises into trivalent iron (Fe³⁺). Trivalent iron gradually precipitates out of the water and forms a rusty turbidity.
In Decree 252/2004 Sb., a maximum concentration of iron of 0.2 mg/L is permitted for drinking water. Increased iron content in water does not pose a health problem, but it can negatively affect the sensory properties of water (colour, odour, turbidity) and its useful properties (discolouration of laundry, sanitary ceramics, clogging of pipes and appliances with precipitated iron, etc.). Long-term consumption of water with iron concentrations above 1 mg/L can cause health problems.

Nitrates (NO^3-)

Increased nitrate content is an indicator of pollution with inorganic nitrogenous fertilisers (fertilisation of fields, gardens, grasslands). In Decree 252/2004 Sb., a maximum nitrate concentration of 50 mg/L is permitted for drinking water, which is further limited to a maximum of 10 mg/L in drinking water for infants.

Nitrites (NO^2-)

Nitrite pollution is mostly associated with an increased content of nitrates (arising from reduction), or accompany pollution of ammonium ions in the case of pollution of faecal origin. In Decree 252/2004 Sb., a maximum concentration of nitrites of 0.5 mg/L is permitted for drinking water.

Sum of calcium and magnesium (‘Total water hardness’)

In Decree 252/2004 Sb., a water hardness range of 2.0 to 3.5 mmol/L is recommended for drinking water, bearing in mind that this is optimal for human health.
Higher hardness does not represent a health problem. Still, the useful properties of water deteriorate due to the formation of so-called limescale; build up in pipes and damage to household appliances occur.
Lower water hardness than 2.0 mmol/L can lead to health problems if it is consumed as the only source of drinking water over the long-term. The body is gradually depleted of calcium and magnesium, substances that must be supplemented from other sources.
The optimal calcium to magnesium ratio is 2:1 to 3:1 in favour of calcium. Long-term use of water with the opposite ratio (predominance of magnesium) limits the use of calcium. Water hardness scale water type total hardness concentration very soft 0-0.7 mmol/L
soft 0.7–1.3 mmol/L medium hard 1.3–2.1 mmol/L quite hard 2.1–3.2 mmol/L hard 3.5–5.3 mmol/L very hard < > 5. 3 mmol/L

Calcium (Ca²⁺)

In Decree 252/2004 Sb., a minimum concentration of calcium of 30 mg/L is recommended for drinking water. For everything else, see total hardness.

Magnesium (Mg²⁺)

In Decree 252/2004 Sb., a minimum concentration of magnesium of 10 mg/L is recommended for drinking water. For everything else, see total hardness.

Manganese (Mn²⁺)

Manganese is often an accompanying element to iron, and its effect on water quality is similar. The increased content of manganese in sources of drinking water (wells) is of natural origin, i.e. the source is the rocks from which the water springs to the surface. Manganese is usually dissolved in water, and in higher concentrations causes greasy circles on the surface of water; if the manganese content is very high, a black deposit forms.
In Decree 252/2004 Sb., a maximum concentration of manganese of 0.05 mg/L is given for drinking water. This value can be up to 0.1 mg/L for natural untreated sources (wells).
5 What do drinking water parameters mean
Increased manganese content in water does not pose a health problem, but it can negatively affect the sensory properties of water (colour, odour, turbidity) and its useful properties (discolouration of laundry, sanitary ceramics, and clogging of pipes and appliances in higher concentrations). Manganese concentrations in water above 1 mg/L can cause health problems if consumed long-term.

Sodium (Na⁺)

Sodium ions in drinking water can either be of natural origin from the bedrock or from road salting.
In Decree 252/2004 Sb., a maximum concentration of sodium ions of 200 mg/L is specified for drinking water. At higher concentrations, the taste of the water is affected.

Chlorides (Cl^-)

Chlorides in drinking water can either be of natural origin from the bedrock, or from sewage pollution or road salting.
In Decree 252/2004 Sb., the maximum concentration of chlorides in drinking water is given as 100 mg/L. This value can be up to 250 mg/L for natural untreated sources (wells).
Higher concentrations of chlorides do not pose a significant health risk, but the sensory properties of the water (taste) are affected. Water with a higher chloride content should not be used by people suffering from hypertension, infants and small children. The high content of chlorides also increases the corrosive effect of water (corrosion of pipes, appliances in which water is used).

Sulphates (SO₄^2-)

Sulphates in drinking water are most often of natural origin from the bedrock, or from water pollution caused by the fertilisation of fields and agriculturally used areas.
In Decree 252/2004 Sb., a maximum concentration of sulphates of 250 mg/L is specified for drinking water. Higher concentrations of sulphates can negatively affect the taste of water, but mainly its useful properties. Sulphates are in most cases in water together with calcium and magnesium and cause so-called permanent hardness of water, which cannot be removed by boiling (for hardness issues see also the keyword hardness). If high levels of magnesium and sulphates are present in water, ingestion of this water can cause diarrhoea.

ANC 4.5 (alkalinity)

ANC 4.5 (acid neutralising capacity) is the quantitatively expressed ability of water to react with hydrogen ions. Depending on the pH of the water, it is mainly caused by bicarbonates and carbonates (so-called bound carbon dioxide).
The value of ANC is not limited by Decree 252/2004 Sb. However, an ANC value above 4.5 is associated with the presence of calcium and magnesium. Hardness in the form of dissolved calcium or magnesium bicarbonate is called transient and can be removed by boiling (scale is formed, which is calcium or magnesium carbonate). For hardness issues see also the keyword hardness.

Fluorides (F-)

Fluorides in drinking water are practically always of natural origin from bedrock. In Decree 252/2004 Sb., a maximum concentration of fluorides of 1.5 mg/L is specified for drinking water.
Water with moderate flouride content is desirable because it contributes to the prevention of tooth decay, especially in children. The optimum fluoride concentration is considered to be in the range from 0.1 to 0.3 mg/L, which is the case for the majority of underground water sources in the Czech Republic.