| 0 | Aluminium | Aluminium is a metal that occurs naturally in soil and rock. In water treatment, aluminium salts can also be used as flocculants.”,”Through natural rock and soil layers, through water treatment with aluminium salts, or through certain materials. At unfavourable pH levels, aluminium can dissolve more easily.”,”Aluminium has no desirable benefits in drinking water. Elevated levels may indicate problems with treatment, pH or turbidity. As a precaution, aluminium levels are kept low for health reasons, particularly in the case of long-term exposure.”,Reverse osmosis membrane: highly effective at reducing dissolved metals. | | | | | |
| Activated carbon: Activated carbon is not the first choice; " | True | 0.20 mg/l, i.e. 200 µg/l. | | | | | |
| 1 | Ammonium | Ammonium is a nitrogen compound. It is produced during the decomposition of organic matter and can occur naturally in groundwater. In drinking water | it is primarily an indicator of potential contamination or treatment problems. | Through natural degradation processes in the soil, but also through sewage, slurry, agriculture, leaking septic tanks, biofilms or oxygen-depleted groundwater. | Ammonium is not as acutely critical as nitrite, but can be an indication of organic contamination or hygiene issues. It can also interfere with water treatment, for example during disinfection, and be converted by bacteria into nitrite and nitrate.”,”Reverse osmosis membrane: may help to reduce levels.
Activated carbon: not usually reliable for ammonium. | True | 0.50 mg/l. |
| 2 | Anion equivalents | Anion equivalents are not a single substance, but a calculated value. It describes the sum of the negatively charged ions in the water, based on their electrical charge. These include, for example, chloride, sulphate, nitrate, hydrogen carbonate, phosphate and other anions. | Anions enter the water via rock, soil, minerals, agriculture, fertilisation, wastewater, industrial discharges or water treatment. The value is determined by the chemical composition of the water. | Anion equivalents are primarily used to check the plausibility of a water analysis. Together with cation equivalents, they can be used to check whether the analysis is chemically consistent. In correctly analysed water, positive and negative charges should largely balance each other out. | Reverse osmosis membrane: reduces many dissolved anions across a very wide range. Activated carbon: does not normally reduce anions reliably. | False | There is no specific limit value for anion equivalents in the Drinking Water Ordinance, as it is not a pollutant but a calculation or control value. |
| 3 | Base capacity up to pH 8.2 | The base capacity up to pH 8.2 describes how much base is required to titrate the water to a pH of 8.2. It is a technical analytical value and not a single substance. BC 8.2 is related to the calcium-carbonate equilibrium, free carbon dioxide, pH value, buffering capacity and corrosion behaviour. The value helps to assess whether water is likely to have an acidic, scale-dissolving or corrosive effect. | An elevated KB 8.2 value may indicate higher levels of free carbon dioxide. This can make water more aggressive towards limescale and materials. This can promote corrosion, the leaching of metals from pipes or technical problems. | No. KB 8.2 is not a pollutant. The value is primarily important for the technical assessment of water, particularly in domestic plumbing systems, water softening, deacidification, reverse osmosis and remineralisation. | Activated carbon: does not normally alter the KB 8.2 value specifically. | False | The Drinking Water Ordinance does not specify a separate limit value for base capacity up to pH 8.2. |
| 4 | Calcium | Calcium is a naturally occurring mineral and is important for bones, teeth, muscles and many bodily functions. Together with magnesium, calcium is one of the main causes of water hardness. | Calcium is released from rock, soil and minerals, particularly from limestone, dolomite or gypsum. This is why some regions have water that is very rich in calcium and hard. | Calcium is not harmful in itself, but is an important mineral. However, from a technical point of view, high levels of calcium can lead to limescale deposits, scale build-up, stains on taps and a build-up of limescale in coffee machines, boilers, household appliances and reverse osmosis systems. | Reverse osmosis membrane: significantly reduces calcium.
Activated carbon: not suitable for targeted calcium reduction. | False | There is no limit value for calcium in the German Drinking Water Ordinance. Nor does water hardness itself have a traditional limit value; it is classified into hardness ranges. The DVGW defines the following hardness ranges: soft below 1.5 mmol/l calcium carbonate, medium between 1.5 and 2.5 mmol/l, and hard above 2.5 mmol/l. |
| 5 | Chlorine | Chlorine is a disinfectant used to kill germs in drinking water. It is therefore not a natural mineral, but a substance used to ensure hygiene. | Through targeted chlorination during water treatment or in the distribution network, for example in the event of microbiological abnormalities, following pipework repairs or for safety disinfection. | Chlorine can cause odour and taste. Furthermore, reactions with organic substances can produce undesirable by-products, such as trihalomethanes, chlorate or chlorite. However, the hygienic benefits are important: chlorine protects against pathogens. | Activated carbon: highly effective against the smell and taste of free chlorine.
Reverse osmosis membrane: reduces many dissolved substances; is usually combined with an activated carbon pre-filter. | False | In Germany, an upper limit of 0.3 mg/l usually applies to free chlorine; in exceptional cases, higher levels of safety chlorination may be authorised by the authorities. |
| 6 | Chloride | Chloride is a naturally occurring salt ion and a component of many minerals, such as sodium chloride. It should not be equated with chlorine as a disinfectant. | Chloride can enter water naturally from rock, soil and minerals. Other sources include road salt, wastewater, industry, agriculture, the influence of seawater or saline inputs into the groundwater. | Chloride is not directly harmful to health in normal quantities. However, elevated levels can lead to a salty taste, corrosion of pipes, material problems and increased strain on the drinking water system. | Reverse osmosis membrane: highly effective at reducing dissolved salts and ions such as chloride.
Activated carbon: not reliable for chloride.
| True | 250 mg/l. |
| 7 | delta-pH | Delta-pH is not a single substance, but a calculated or evaluative value. It describes the difference between the measured pH value of the water and a calculated equilibrium pH value.
Put simply, delta-pH indicates whether water is in the calcium-carbonic acid equilibrium. | The value helps to assess whether water is more likely to:
promote limescale formation, i.e. tend to form limescale deposits,
or act as a limescale-dissolving/corrosive agent, i.e. could cause greater damage to materials and pipework.
delta-pH is therefore particularly important for assessing corrosion, pipework, fittings, limescale formation, water softening, reverse osmosis and remineralisation. | No. delta-pH is not a pollutant. However, an abnormal value may indicate a technical risk:
Water that dissolves limescale too vigorously can promote corrosion and thereby leach metals such as copper, nickel or lead from the system.
Water that causes excessive limescale formation can lead to limescale deposits, build-up and technical problems. | Activated carbon: does not normally have a specific effect on delta-pH. | False | There is no standard pollutant limit for delta-pH in the Drinking Water Ordinance. The value is assessed more in the context of calcite dissolution capacity, pH value, hardness, hydrogen carbonate and corrosion behaviour. |
| 8 | Iron | Iron is a naturally occurring metal and an important trace element. In drinking water, it does not usually pose an acute health risk, but can cause technical and aesthetic problems. | Particularly due to iron-bearing rock and soil layers, groundwater, old pipes, corrosion or deposits within the plumbing system.”,”Elevated iron levels can lead to a rust-brown colour, a metallic taste, turbidity, deposits and discolouration on taps, laundry or sanitary surfaces. Furthermore, iron can promote the formation of biofilms and cause technical problems in filters, pipes or systems. | Reverse osmosis membrane: can reduce iron, but should not be exposed directly to water with a high iron content, as this can cause the membrane to become clogged.
Activated carbon: not the first choice | True | 0.200 mg/l, i.e. 0.2 mg/l. | |
| 9. Electrical conductivity | Electrical conductivity indicates how many dissolved ions, minerals and salts are present in the water. The more dissolved substances such as calcium, magnesium, sodium, chloride or sulphate there are, the higher the conductivity usually is. | This is caused by dissolved minerals from rock, soil and salts. However, it can also be increased by road salt, the influence of seawater, sewage, industrial discharges, agriculture or technical treatment. | Conductivity is not a single pollutant, but a summary and monitoring parameter. It provides an indication of mineralisation, salinity, water hardness, possible inputs or changes in the water. It is particularly important in reverse osmosis systems because it provides a good indication of the extent to which dissolved substances are reduced. | Reverse osmosis membrane: highly relevant, as it significantly reduces dissolved ions and salts.
Activated carbon: normally reduces conductivity only slightly. | True | Under the German Drinking Water Ordinance | the value for electrical conductivity is 2 |
| 10 | Colour | Colour describes whether drinking water has a visible or measurable discolouration. Drinking water should generally appear clear and colourless. | Possible causes include iron, manganese, humic substances, organic substances, algae components, corrosion, deposits in pipes, or inputs from soil and surface water. | Colour is usually not a direct contaminant, but an important indicator. It can point to treatment problems, corrosion, organic contamination, iron/manganese issues or impurities. It also affects the appearance, trust in and acceptance of the drinking water. | Reverse osmosis membrane: can significantly reduce dissolved and organic components. Activated carbon: effective for organic substances, humic substances, and odour and taste problems. | True | Under the German Drinking Water Ordinance, the value for colour, based on the spectral absorption coefficient at 436 nm, is 0.5 1/m. |
| 11 | dissolved oxygen | Dissolved oxygen is oxygen gas dissolved in water. It is a natural component of many types of water and is important for the chemical stability of the water.”,”Primarily through contact with the air, water movement, natural aeration and technical treatment. Groundwater may contain little oxygen, depending on depth and geological conditions.”,”Dissolved oxygen is not a pollutant. However, it indicates whether water is more oxidising or reducing. Water low in oxygen is often associated with elevated levels of iron, manganese or ammonium. Water rich in oxygen, on the other hand, can influence corrosion processes in certain installations. | Reverse osmosis membrane: does not specifically remove dissolved oxygen.
Activated carbon: not suitable for targeted oxygen regulation. | False | The German Drinking Water Ordinance does not specify a separate limit value for dissolved oxygen. It is used more as a technical and hydrochemical assessment parameter. Values above 4 mg/l certainly indicate an oxidising environment. | | |
| 12 | Odour | Odour is a sensory indicator. Drinking water should have a neutral, fresh and unobtrusive odour.”,”Possible causes include chlorine/disinfectants, biofilm, stagnation, organic matter, algae, sulphur compounds, iron/manganese, pipe materials, and odours from sewage or soil.”,”Odour is usually not caused by a single contaminant, but can be an important indication of hygiene issues, treatment errors, stagnation, biofilm or chemical contamination. Musty, putrid, chlorinated or chemical odours should therefore always be taken seriously.”,Activated carbon: highly effective against many odour- and taste-causing substances | chlorine and organic compounds. Reverse osmosis membrane: can reduce many dissolved substances | but should be combined with pre-filtration depending on the cause." | True | The Drinking Water Ordinance defines odour as: ‘acceptable to the consumer and without any abnormal changes’ | |
| 13 | Total Organic Carbon (TOC) | “TOC stands for Total Organic Carbon | i.e. the total amount of organically bound carbon in the water. It does not indicate a single contaminant | but rather the total amount of organic substances in the water.” | “This can result from natural organic matter in soil | plant residues | humic substances and surface water |
| 14 | Taste | Taste is a sensory indicator. Drinking water should taste fresh, neutral and pleasant. | Possible causes include chlorine or disinfectants, high mineralisation, sodium, chloride, sulphate, iron, manganese, copper, biofilm, stagnation, pipe materials, organic substances or treatment residues. | “A noticeable taste is not automatically dangerous | but may indicate changes in water quality | corrosion | stagnation |
| Reverse osmosis membrane: reduces a very wide range of dissolved substances | salts | metals and residues." | True | The Drinking Water Ordinance defines taste as: ‘acceptable to the consumer and without any abnormal changes’. It is monitored because it quickly indicates whether water quality, the installation or the treatment process has changed. | | | |
| 15 | Ion balance | The ion balance is a plausibility check in a water analysis. It compares the sum of the positively charged ions, i.e. cations, with the sum of the negatively charged ions, i.e. anions.
Cations include, for example, calcium, magnesium, sodium and potassium.
Anions include, for example, chloride, sulphate, nitrate and bicarbonate.”,,”Water must be largely electrically neutral. This means that, in mathematical terms, the positive and negative charges should roughly balance each other out. If the ion balance deviates significantly, this may indicate measurement errors, missing parameters, incorrect units or incomplete analysis values.”,Reverse osmosis membrane: broadly reduces cations and anions, thereby lowering the total mineralisation.,False,There is no specific limit value for the ion balance in the Drinking Water Ordinance | as it is not a pollutant but a control and calculation value." | | | | |
| 16 | Cation equivalents | Cation equivalents are not a single substance, but a calculated value. It describes the sum of the positively charged ions in the water, based on their electrical charge. These include, for example, calcium, magnesium, sodium, potassium, iron, manganese, ammonium and other cations. | Cations enter the water primarily via rock, soil, minerals, corrosion, agriculture, wastewater, industrial discharges or water treatment. The value is determined by the chemical composition of the water. | Cation equivalents are primarily used to check the plausibility of a water analysis. Together with the anion equivalents, they are used to verify whether the analysis is chemically consistent. In water, positive and negative charges must largely balance each other out. | Reverse osmosis membrane: reduces many dissolved cations across a very wide range. Activated carbon: not the first choice for many cations, unless special adsorption media are used. | False | There is no specific limit value for cation equivalents in the Drinking Water Ordinance, as they are not a pollutant but rather a calculation and control value. |
| 17 | Colony count at 22 °C | The colony count at 22 °C indicates how many viable microorganisms can grow in the water when the sample is incubated at 22 °C. It is not a specific pathogen, but a general indicator of hygiene and system performance. | They may occur naturally in the water or be elevated due to biofilm, stagnation, deposits, pipework, filters, fittings, storage tanks, containers or treatment problems. | An elevated colony count does not automatically mean that the water is hazardous. However, it may indicate the presence of biofilm, stagnation, inadequate flushing, technical problems or microbiological growth. Sudden changes compared with previous readings are particularly noteworthy. | Adhere to replacement intervals, particularly for activated carbon filters. | True | In many cases |
| 18 | Colony count at 36 °C | The colony count at 36 °C indicates how many viable microorganisms can grow in the water when the sample is incubated at approximately body temperature. It does not represent a single pathogen, but rather a microbiological hygiene and indicator parameter. | Possible causes include biofilm, stagnation, warm sections of pipework, storage tanks, fittings, filters, deposits or treatment problems. As 36 °C is close to body temperature, this value is of particular interest from a hygiene perspective. | An elevated colony count at 36 °C does not automatically mean that pathogens are present. However, it may indicate hygiene issues, biofilm growth, stagnation or unfavourable temperatures. A sudden or significant change compared with previous readings is particularly critical. | Adhere to replacement intervals, particularly for activated carbon filters. | True | The colony count at 36 °C is an indicator parameter under the Drinking Water Ordinance. In many cases |
| 19 | Magnesium | Magnesium is a naturally occurring mineral and an important trace element for the body. Together with calcium | it contributes to water hardness. | Mainly through rock, soil and minerals, from which magnesium dissolves into the groundwater. Depending on the region, the magnesium content can vary considerably. | Magnesium is not harmful in itself, but is an important mineral. In drinking water, it is usually more of a quality and hardness parameter. High magnesium and calcium levels make water harder and can lead to limescale deposits, increased cleaning requirements and wear and tear on appliances. | Reverse osmosis membrane: reduces magnesium very significantly.
Activated carbon: unsuitable for the targeted reduction of magnesium. | False |
| 20 | Manganese | Manganese is a naturally occurring metal and | in very small quantities | an important trace element. In drinking water | however | it is primarily an indicator parameter and is of technical relevance. | Mainly due to manganese-containing rock and soil layers, oxygen-depleted groundwater, well water or deposits in pipes and systems. |
| 21 | Sodium | Sodium is a naturally occurring mineral and a component of many salts, such as sodium chloride. It is an important electrolyte for the body. | Sodium can enter water naturally from rock, soil and minerals. Other sources include road salt, seawater inflow, wastewater, industry or water softening systems, in which calcium and magnesium are exchanged for sodium. | In normal quantities, sodium is usually not a problem. However, elevated levels may be of concern for people who need to follow a low-sodium diet, for example those with certain heart, kidney or blood pressure conditions. Furthermore, very high levels of sodium can affect the taste. | Reverse osmosis membrane: highly effective at reducing sodium and other dissolved salts.
Activated carbon: not reliable for sodium. | True | 200 mg/l. |
| 22 | Oxidisability | Oxidisability is a summary parameter. It indicates how many substances are present in the water that can be chemically oxidised. These include primarily organic substances, but in some cases also certain inorganic substances. | Possible causes include humic substances, plant residues, organic contaminants, the influence of surface water, wastewater, biofilm, algal components or treatment problems. | Oxidisability is usually not a direct indicator of pollutant levels, but rather an indication of organic load. Elevated values may indicate contamination or changes in the water. Furthermore, organic substances can form undesirable by-products during disinfection, such as trihalomethanes. | Activated carbon: highly effective at reducing many organic substances.
Reverse osmosis membrane: broadly reduces many dissolved organic and inorganic substances. | True | 5.0 mg/l O₂. However, this parameter can only be determined if the TOC value is not measured. |
| 23 | pH value | The pH value indicates whether water is acidic, neutral or alkaline. A pH value of 7 is considered neutral. Values below this are acidic; values above are alkaline. | It is influenced by rock, minerals, carbon dioxide, treatment, softening, deacidification and water chemistry. The calcium-carbonate equilibrium also plays a major role. | The pH value is not so much a direct indicator of contamination as an important technical stability parameter. A pH value that is too low can make water more corrosive and thus cause metals such as copper, nickel or lead to leach more easily from pipes. A pH value that is too high can affect taste, cause limescale build-up and impact water treatment. | Reverse osmosis membrane: often reduces mineralisation and can make the water less buffered; it is frequently remineralised afterwards.
Activated carbon: does not normally alter the pH value in a targeted manner. | True | Under the German Drinking Water Ordinance, the permissible range is pH 6.5 to 9.5. |
| 24 | SAK 436 nm (colour, quant.) | SAK stands for spectral absorption coefficient. At 436 nm, the extent to which water absorbs visible light at this wavelength is measured. The value therefore describes the quantitative colour of the water. | Possible causes include humic substances, organic matter, iron, manganese, algal components, corrosion, deposits, the influence of surface water or treatment problems. | SAK 436 nm is not a single contaminant, but an indicator parameter. Elevated values may indicate organic contamination, metal compounds, turbidity, impurities or technical problems. Drinking water should be visually clear and colourless. | Activated carbon: relevant for organic substances, humic substances, and odour and taste compounds. Reverse osmosis membrane: can significantly reduce dissolved and organic constituents. | True | In the Drinking Water Ordinance, the value for colour / SAK 436 nm is 0.5 m⁻¹. The measurement is carried out using a spectrophotometer or filter photometer at 436 nm. |
| 25 | Calcite saturation index (SI) | The calcite saturation index, often referred to as SI, is a technical assessment value. It indicates whether water is in equilibrium with calcium carbonate / lime.
Put simply, the SI indicates whether water tends to dissolve lime, is stable, or precipitates lime. | The SI is important for assessing:
Corrosion
Lime formation
Pipes and fittings
Hot water systems
Water softening
Reverse osmosis and remineralisation
Calcite dissolution capacity
How is the SI interpreted?
SI < 0: The water is undersaturated and may dissolve limescale. This can promote corrosion.
SI ≈ 0: The water is in a lime-carbonic acid equilibrium.
SI > 0: The water is supersaturated and is more prone to limescale deposits. | The SI value itself is not a pollutant. However, an unfavourable SI value can have technical consequences. Water that dissolves limescale can attack pipes and thereby leach metals such as copper, nickel or lead from the system. Water that precipitates limescale can lead to limescale build-up, deposits and damage to appliances. | Reverse osmosis membrane: significantly reduces mineral content and often makes downstream stabilisation advisable.
Activated carbon: does not normally have a specific effect on the SI. | False | The Drinking Water Ordinance does not specify a standard limit value for the calcite saturation index |
| 26 | Dissolved oxygen (O₂) | Dissolved oxygen is oxygen gas dissolved in water. It is not a pollutant, but a natural and technical water parameter. | Through contact with air, movement, aeration, treatment or natural oxygen uptake. Groundwater from deeper or oxygen-poor layers often contains less oxygen. Dissolved oxygen influences water chemistry. Water with low oxygen levels is more frequently associated with iron, manganese, ammonium or reducing conditions. In contrast, oxygen-rich water can influence corrosion processes in pipes and fittings.”, “No. Dissolved oxygen is not harmful. However, it is important for assessing corrosion, biological stability, iron/manganese behaviour and water treatment. | Reverse osmosis membrane: does not specifically remove oxygen.
Activated carbon: not suitable for targeted oxygen regulation. | False | The Drinking Water Ordinance does not specify a separate limit value for dissolved oxygen. | |
| 27 | Sulphate | Sulphate is a naturally occurring salt of sulphuric acid. It is found in many rocks and minerals and is a normal component of many types of water. | Primarily from rock, soil and minerals. In addition, sulphate can enter the water via agriculture, fertilisation, industry, sewage, mining or acid rain. | In normal quantities, sulphate is usually not a problem. However, elevated levels can lead to a bitter taste, corrosion, technical problems and, at very high levels, a laxative effect.”, “Reverse osmosis membrane: highly effective at reducing dissolved salts and ions such as sulphate.
Activated carbon: not reliable for sulphate. | True | 250 mg/l. | |
| 28 | Temperature | Temperature describes how warm or cold the drinking water is when it is supplied. It is not a contaminant, but a very important hygiene and technical parameter. | Due to the season, pipe length, stagnation, poorly insulated pipes, proximity to heating pipes, hot-water systems, storage tanks, circulation or long periods of inactivity. | Cold water that is too warm can promote microbial growth. The range in which germs and biofilms can multiply more easily is particularly critical. For hot water, a sufficiently high temperature is important to reduce the risk of Legionella. | Activated carbon and reverse osmosis membranes: do not specifically alter the temperature. | True | The Drinking Water Ordinance does not list temperature as a standard limit parameter in Annex 3. In practice, technical requirements apply: cold water should not exceed 25 °C after 30 seconds at the latest, whilst hot water should reach at least 55 °C; 60 °C is often specified for drinking water heaters. |
| 29 | Turbidity | Turbidity describes how clear or ‘cloudy’ water is. It is caused by minute suspended solids, particles, minerals, rust, clay, limescale, organic matter or microorganisms. | Possible causes include construction work on the distribution network, pipe deposits, corrosion, iron/manganese, limescale deposits, inflow of surface water, biofilm or problems in water treatment. | Turbidity is usually not a single contaminant, but an important indicator. It may indicate the presence of particles, hygiene issues or treatment faults. Furthermore, particles can shield pathogens and reduce the effectiveness of disinfection or UV treatment. | Reverse osmosis membrane: reduces particles and dissolved substances, but should be protected from high turbidity by pre-filters.
Activated carbon: can also reduce organic substances, but is not a conventional turbidity filter.
| True | According to the German Drinking Water Ordinance, the turbidity limit is 1.0 NTU. |
| 30 | Water hardness | Water hardness primarily describes the content of calcium and magnesium compounds in the water. The more of these it contains, the ‘harder’ the water is. Values: very soft 0–4 °dH, soft
4–8.4 °dH, medium-hard 8.4–14 °dH, hard 14–21 °dH, very hard over 21 °dH
| Water absorbs minerals as it passes through soil and rock. In calcareous regions in particular | large amounts of calcium and magnesium dissolve into the groundwater. | Water hardness is not usually a health concern. Calcium and magnesium are, in fact, important minerals. Technically, however, hard water can lead to limescale build-up, stains on taps, increased cleaning effort and wear and tear on coffee machines, boilers, household appliances and reverse osmosis systems. | Reverse osmosis membrane: significantly reduces calcium, magnesium and many other dissolved substances.
Activated carbon: not suitable for targeted water softening. | False |
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