Water analysis

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Water analyzes are used to determine chemical, physical and microbiological parameters that describe the nature of the respective sample. Such analyzes are carried out, for example, when evaluating groundwater , medicinal water , spring water and the like. Water analyzes of drinking and raw water are of particular importance . The number and scope of the analyzes are required by law in many countries, and in Germany by the Drinking Water Ordinance . Another important area of ​​application is fishing .

Most often, water is examined for chloride , sulfate , nitrate , nitrite , ammonium , the pH value , the oxygen content , the electrical conductivity , the phosphate content and the water hardness . The so-called sum parameters are also frequently examined . This includes, for example, the organic load, i.e. the TOC , the chemical oxygen demand or the oxidisability by potassium permanganate and the biological oxygen demand .


The type of sampling of water is usually based on the requirements of the sample, i.e. it depends on the parameters to be determined. Some of them still have to be determined during or at least immediately after sampling, as the values ​​would change in the course of storage. These include temperature and pH value, the oxygen content, but also odor , turbidity and the like. In spring water, agitated sediment and particles floating on the surface must not get into the sample vessel. At the same time, damming or lowering the spring water level should be avoided.

Clean, colorless glass or polyethylene bottles serve as vessels, which should be rinsed several times with the water to be examined before the analysis. The bottles are closed with stoppers or screw caps made of the same material for transport. If organic pollution such as PAHs ( polycyclic aromatic hydrocarbons ) are also to be examined, metal vessels are also suitable, whereby chemical reactions between the bottle and the water sample are to be excluded.

The taking of the sample only begins when the water is no longer affected by external influences, i.e. can be regarded as representative of the water body to be examined. In general, this state is reached when the electrical conductivity is constant.

In the areas of drinking water analysis, so-called stagnation samples are taken to determine heavy metal pollution. Here, the line is first rinsed for about 5 minutes (until the temperature is constant) with the tap turned on and a first 1 liter fraction is taken as a so-called SO sample. The analysis of this sample enables an assessment of the water quality supplied by the drinking water supplier. The tap is then closed and no more water is withdrawn, ideally in the entire building. After a waiting time of 4 hours on average (stagnation), two more one-liter samples are taken one after the other. The first fraction (S1 sample) provides information about the heavy metals released by the fittings during the analysis. As a rule, there are increased nickel and lead concentrations here. The content of the following second 1L fraction (S2 sample) is examined for heavy metals which are released into the drinking water through the water pipes of the house installation. The stagnation gives the water the opportunity to react with the metals. The concentration of heavy metals provides information about the state of corrosion and material properties of the fittings and pipes used. This method can be used, for example, to check whether lead installations have been laid without having to open wall openings or inspect the basement.

Field analysis

Organoleptic and physicochemical parameters are determined on site. For organoleptic properties include odor, color, turbidity, sediment and samples of drinking water quality of taste. The physicochemical parameters of water temperature, pH value, oxygen content and redox potential as well as the total gas saturation can only be measured correctly in situ, as they depend not only on the components of the sample but also on the environment. So if at all possible, these values ​​should be determined on site at the time of sampling. In addition to these parameters, the carbon dioxide must also be determined as soon as possible after the sampling (especially the pH measurement required for this).

Water temperature, electrical conductivity and pH value

These three parameters are determined using a multimeter, for example. For this purpose, the appropriate measuring sensors are attached to the device and, if necessary, calibrated before the measurement.

The electrical or specific conductivity indicates how much current is transported in a solution by anions and cations, so it is a measure of the ions dissolved in the water . The measurement is carried out using a conductivity meter and is specified in the unit µS / cm. As a rule of thumb , one can say that 90 µS / cm (at 25 ° C) corresponds to a carbonate hardness of 1 mEq / L (2.8 ° dH), with about 80 ± 60 µS / cm being due to other ions. Otherwise, the measured value is a measure of the exposure to dissolved salts . For surface water, a value between 500 and 1000 µS / cm often applies. Higher values ​​indicate excessive exposure (e.g. sodium chloride ).

The pH value is defined as the negative decadic logarithm of the activity (in mol / L) of H + ions and is a measure of the acidic or alkaline character of solutions. If the pH value is determined electrometrically , this means that a potential difference is measured using a combination electrode of a pH meter and the pH value is automatically calculated from this. Before the measurement, the device must be calibrated using buffer solutions with defined pH values ​​(e.g. 4, 7, 9). The pH value should be around 7 in natural waters. Smaller values ​​(e.g. between 3 and 6) indicate exposure to acids , higher values ​​(above 8) indicate exposure to bases .

Analysis of chloride ions

Normal surface water and groundwater contain 10–30 mg Cl - / L. However, the value can be much higher near coasts. The chloride content can also be greatly increased in the vicinity of salt deposits. Likewise, due to the potash industry, the wastewater produced there and thus the rivers can have a higher chloride content. A chloride content greater than 250 mg Cl - / L gives the water a salty taste. The edibility limit is around 400 mg Cl - / L, although this content is physiologically harmless. A high chloride content also promotes the corrosion of iron pipes and fittings. Desalination should be considered for service water . Usually the chloride content is due to sodium chloride . 400 mg Cl - / L correspond to about 660 mg / L dissolved sodium chloride.

The determination of the chloride ions can be carried out titrimetrically using the argentometry method .
The mercury (II) nitrate method can be used for small amounts of
chloride : Here the water sample is titrated with an Hg (NO 3 ) 2 solution with a concentration of 0.01 mol / L and the indicator diphenyl carbazone. Undissociated mercury (II) chloride is formed with the chloride ions . At the end of the titration, the indicator reacts with excess Hg 2+ ions from the Hg (NO 3 ) 2 solution to form a purple complex compound.

Analysis of sulfate

Normal water has a sulfate content of up to 50 mg SO 4 2− / L. In certain areas (e.g. brown coal areas) the sulphate content can be significantly higher. Contaminated water can also have a significantly higher sulphate content. The sulphate content is mainly due to dissolved gypsum . Sulphate-rich water is harmful to concrete structures. Water with a high sulphate content (greater than 250 mg / L), especially due to sodium sulphate , has a laxative effect. Sulphate is the main component of non-carbonate hardness .

Sulphate ions can be determined with sufficient accuracy using the following method: Here, the turbidity is determined photometrically after addition of barium chloride solution (precipitation of barium sulphate ) . If a photometer is not available, a visual determination can also be made, albeit with greater inaccuracy. For comparison, barium sulfate is precipitated from a sulfate solution with a known concentration.

For water with a sulphate content greater than 100 mg / L, the gravimetric method after precipitation as barium sulphate is recommended.

Sulphates can be determined titrimetrically with barium perchlorate solution and thorine as indicators: During titration, barium sulphate is formed as long as sulphate ions are present. At the end point, thorin reacts with excess barium ions to form a red-orange complex compound . Before doing this, however, metal cations must be removed using an ion exchanger , because they would react with thorin.

Analysis of oxygen

Surface waters often contain oxygen to the point of saturation (9.2 mg / L at 20 o C, 14.5 mg / L at 0 o C). Occasionally, however, plankton activity can lead to oversaturation. On the other hand, the oxygen can decrease through anaerobic processes. For fish there should be an oxygen content of at least 5 mg / L. Pure groundwater is usually free of oxygen.

The determination is carried out according to the Winkler method or electrochemically with an oxygen electrode .

Analysis of hydrogen carbonate

To determine the hydrogen carbonate (HCO 3 - ), the acid capacity must usually first be determined. The acid capacity (KS 4.3 or acid binding capacity "SBV") is the ratio of the amount of substance of hydronium ions n (H 3 O + ) that can absorb a corresponding amount of water until the pH value is reached, to their volume V (H 2 O) defined. In contrast to the SI unit [mol / m³], the unit chosen is usually [mmol / L] or the equivalent amount [meq / L].

To determine the acid capacity, hydrochloric acid with a concentration of 0.1 mol / L is titrated in a specific sample volume, usually 100 ml, after a few drops of Cooper indicator have been added to it. The color change from steel blue to sun yellow occurs when the required pH value of 4.3 is reached. Traditionally, methyl orange is used as an indicator , which also changes at pH 4.3. This is why this acid capacity was also referred to as the "m value". If the content of cations of the alkaline earth metals , i.e. the total hardness, is greater than this value, the acid capacity determined in this way corresponds to the carbonate hardness and is converted into "degrees of German hardness" (° dH) with a factor of 2.8 from mEq / L.

The acid capacity is calculated using the formula

KS 4.3 [mol / L] = V (hydrochloric acid) [ml] · c (hydrochloric acid) [mol / L] / sample volume [ml]

The hydrogen carbonate concentration is then calculated from the amount of hydrochloric acid used. To do this, the amount of hydrochloric acid that is responsible for the pH value 4.3 must first be deducted, namely 0.05 mmol / L. The formula is used for the calculation

HCO 3 - = (KS 4.3 - 0.05 mmol / L) · 61.017 g / mol

where 61.017 g / mol is the molar mass of hydrogen carbonate ( HCO 3 - ).

Alternatively, the concentration of the hydrogen carbonate can also be determined by ion HPLC or by capillary electrophoresis .

Analysis of free carbon dioxide

The total free carbonic acid (CO 2 ) of a water sample is determined by titration up to a pH value of 8.2 [KB 8.2 ] (determination of the base capacity ), which is visible, for example, through a color change of phenolphthalein from colorless to pink (this The indicator method is very imprecise; better: pH meter). At this point the previously free carbonic acid is completely converted into hydrogen carbonate (HCO 3 - ) according to the dissociation equilibrium of the carbonic acid .

In water engineering, a positive or a negative p-value is given in mval / L or mmol / L for the content of carbonic acid or carbonate (or alkaline solutions), depending on whether the pH is 8.2 or lower or from higher initial pH values ​​(and accordingly with alkali or acid as Titrand). (The "p" is derived from the indicator phenolphthalein.) A negative p-value indicates the content of free CO 2 in a water, while a positive p-value the content of carbonate (or OH - ions, if applicable from other free ones Lye).

The analysis of the mostly low CO 2 concentrations is more precise, however, usually through a precise determination of the acid capacity and the pH value of the water sample, with subsequent calculation of the CO 2 according to the dissociation equilibrium of the carbonic acid. The temperature and the electrical conductivity must be taken into account as a representative of the ionic strength.

Analytics in the treatment of water for technical purposes

In contrast to the analysis of drinking water, when treating water for technical purposes, only a few parameters are important for assessing water. Knowledge of the trace element content in raw water is normally unimportant.

For the design, control and monitoring of technical systems for deacidification , decarbonisation , softening or partial and full desalination , only the values ​​for the various positive and negative m and p values ​​(named after the indicator used, methyl red / methyl orange and phenolphthalein ), the Total hardness, the content of silicon dioxide (SiO 2 ) and the oxidisability ( potassium permanganate consumption ) of the water are required.

Note: In technology, the unit mval / L is still predominantly used instead of mmol / L, as this means that precise knowledge of the valency of the ions can be dispensed with. The m and p values ​​are therefore often given in mval / L. In the summation of ions but then must either only with meq / L or be expected mmol / L.

The following table contains more detailed information on the individual values, their respective meaning, calculation and one of the commonly used analysis methods:

Analysis value / ion group Type of ions in the water sample 1st dimension 2nd calculation one of the usual analytical methods

+ m value

  • mval / L or mmol / L
  • is measured directly

- p-value

  • mval / L or mmol / L
  • is measured directly

Non-carbonate hardness

  • Breakdown of total hardness into non-hardness and carbonate hardness

- m-value

  • indicates the sum of the content of strongly acidic anions (Cl, SO 4 , NO 3 )
  • mval / L or mmol / L
  • by adding the values ​​of the strongly acidic anions
  • if not calculated by determining the - m-value from a water sample that was passed through a strongly acidic cation exchanger

Sodium and potassium

  • Determination of the sum of the alkalis
  • mval / L or mmol / L
  • (- m-value plus + m-value) minus total hardness

KMnO 4 value

  • gives the content of the org. Substances (e.g. humic acids)
  • mg KMnO 4 / L
  • is measured directly

SiO 2 value

  • indicates the content of compounds of silica as SiO 2 at
  • mg / L
  • is measured directly

With the values ​​listed, the content of a natural water is recorded for all different ingredients. The + p value that is not listed indicates the content of OH - ions in the water. This is, for example, the excess of calcium hydroxide in decarbonised water. With the exception of the rare soft water with a sodium hydrogen carbonate content, this value can only occur in chemically treated and not in natural water.

The total sum of cations and anions in the respective water is calculated using these values ​​as follows:

  • Sum of the cations = + m-value plus - m-value
  • Sum of the anions = + m-value plus - p-value plus - m-value plus SiO 2 content

For the design and operational monitoring of partial and full desalination plants, the contents of carbonates and weakly acidic anions are often calculated separately. This is also possible with the values ​​above.

Knowledge of the KMnO 4 and SiO 2 contents are important for the design and choice of ion exchange resins in a desalination plant.

Web links


  • Walter Kölle: Water analyzes - judged correctly - basics, parameters, water types, ingredients, limit values ​​according to the Drinking Water Ordinance and the EU Drinking Water Directive. Wiley-VCH, Weinheim 2004, ISBN 3-527-30661-7 .
  • Leonhard A. Hütter: Water and water investigation - methodology, theory and Practice of chemical, chemical-physical, biological and similar bacteriological test methods. Sauerländer, Frankfurt 1994, ISBN 3-7935-5075-3 .
  • Hans H. Rump, H. Krist: Laboratory manual for the investigation of water, waste water and soil. VCH, Weinheim 1992, ISBN 3-527-28414-1 .
  • Leo ML Nollet: Handbook of Water Analysis. Marcel Dekker, New York 2000, ISBN 0-8247-8433-2 .
  • Philippe Quevauviller, K. Clive Thompson: Analytical methods for drinking water - advances in sampling and analysis. Wiley, Chichester 2006, ISBN 0-470-09491-5 .
  • Thomas R. Crompton: Analysis of seawater - a guide for the analytical and environmental chemist. Springer, Berlin 2006, ISBN 3-540-26762-X .
  • Karl Höll: Water: Use in the cycle, hygiene, analysis and evaluation . Walter de Gruyter, 2002, ISBN 3-11-012931-0 ( limited preview in the Google book search).

Individual evidence

  1. Stagnation samples in water analysis: Staggered sampling to determine heavy metal pollution (PDF file; 345 kB).
  2. Assessment of the drinking water quality with regard to the parameters lead, copper and nickel: Recommendation of the Federal Environment Agency (PDF file; 139 kB).