Skoči na glavno vsebino


Source of instructions: Nacionalni inštitut za javno zdravje

Boiling drinking water is a precaution of preparing drinking water by which remove microbiological contamination is removed. In general, this is a short-term measure. It is necessary to take it in order to protect the health of people if the use of drinking water might be a potential threat to their health.

Instructions for boiling the water

Once the water reaches a rolling boil, let it boil for one minute. As the conditions for functioning of the germs change depending upon the altitude level, you should increase the rolling time to ensure greater safety. It is recommended to let the water boil for three minutes. Boiling kills and deactivates vegetative forms of pathogenic bacteria, viruses and also giardia and Cryptosporidium cysts. Three minutes of boiling ensure the safety level to that degree that also people with severely weakened immunity can consume such water (e.g. AIDS patients).


In order to prevent additional pollution of the boiled water, it is recommended to keep it in the same vessel where you boiled it. Keep it in the fridge, in a clean and covered vessel. You can use this water for drinking up to 24 hours, exceptionally 48 hours.

If the tap water is cloudy, you should remove most of the particulates before boiling. This can be achieved by sedimentation and then filtration through several layers of a clean, possibly ironed cloth, or a clean paper filter (e.g. blotting paper, coffee filter).

 Prekuhavanje vode, vrenje vode


Since boiled water might have a rather unpleasant taste, it is recommended that tea or other drinks are made from it, or that it is used in soup or another dish.




  • Disinfecting drinking water by boiling is a safe method.
  • Three minutes of boiling ensure water safety.
  • If the water is cloudy, clarify it before boiling by sedimentation and then filtration.
  • Prevent the possibility of additional contamination of the water.
  • Keep boiled water in a place with a cool temperature.
  • Use boiled water for drinking up to 24 hours, exceptionally 48 hours.


Through the process of cleaning the house-water-network at least once yearly, the growth of bacterial biofilms can be avoided.

Care for the high quality of drinking water in schools and food industry

In the food industry in which foodstuffs are produced and sold (restaurants facilities, school kitchen and other kitchens, stores, cake shops, bake-houses, delicacies, food production…), care for the high quality of drinking water should be regularly taken, both in the internal water network, and inside the house. For this reason we recommend the regular control of the quality of drinking water in the internal water network, and a regular cleaning process for all water pipes and all taps. 


For water that is used without any previous treatment (natural water, without disinfection) we recommend:


  • The water should flow out of all taps that are used for hand washing and personal hygiene, food washing and cleaning, or where the water is used as a raw material, before the work starts, at least 2 minutes or so or long enough for the water temperature to stabilize (so that it doesn’t drop any further).
  • At least every 14 days, taps should be removed and cleaned.
  • On every tap, or at least on one tap in the house, once each year a drinking water sample should be taken, and a microbiological examination should be performed. At the same time a sample of input water should be taken (before or after the counter)
  • If the food premises are connected to a water system where the quality of the drinking water oscillates, at least one yearly all the taps and the entire internal network should be disinfected (chlorine shock). The same process is recommended when the premises or network has been restored or reconstructed.
  • If a chlorine shock isn’t possible, we recommend the cleaning of the internal network, which should be done at least twice yearly. The chlorine should remain in the water for at least two days at a concentration of free chlorine in the water of between 0.2 and 0.4 mg/Litre of water.
  • A record of the maintenance, cleaning, disinfection, interventions, samples and results should be kept and archived.


For that is to be used after a previous treatment (water that has just been disinfected) we recommend the following:

  • The water should flow out of all taps (sinks) that are used for hand washing or personal hygiene, food washing, cleaning or where the water is used as a raw material, before work is due to start, by at least 2 minutes or long enough for the water temperature to stabilize (so that it doesn’t drop any further) – for example, every morning before work begins, especially on Mondays, when the establishment hasn’t been in use over the weekend and the water in the pipes has not flowed.
  • At least every 14 days on all taps should be removed and cleaned.
  • On every tap, or at least on one tap in the house once yearly, a drinking water sample should be taken and a microbiological examination should be performed. At the same time a sample of input water (before or after the counter) should be taken.
  • During the restoration work on the premises or on the network, disinfection should be done (chlorine shock) on the internal network, and on the taps.
  • A record of the maintenance, cleaning, disinfection, interventions, samples and results should be kept and archived.


If in the internal network there is a water cleaning filter, it should be maintained, cleaned and changed very carefully and regularly. Its functioning should also be controlled regularly. Microbiological examination of drinking water samples should be done before and after filtration. If the filters have not been maintained well enough or regularly enough, the microbiological quality of the water and the safety of the drinking water could be worse. A poorly-maintained filter becomes a source of infections with microorganisms.


For further information you can ask the contractor of the water system that supplies your school or premises.

A poorly-maintained filter can become a source of infection with microorganisms, and can contaminate the drinking water from the water system.

Prevent water meters from freezing

During cold winter months, the air temperatures are very low and often cause damage to pipes and meters. Frozen meters may break down – burst. That is why you should protect them from such weather conditions with appropriate thermal protection and occasional water flow.


 Zmrzal na vodovodnem priključku


The water supplier is not responsible for such damage, as the meters are owned by their users who should protect the installed meters by providing thermal insulation to the meters and water-meter shafts.


We therefore advise especially all users who do not permanently reside in the buildings where plumbing is installed (e.g. holiday homes, weekend cottages etc.) to periodicallycheck water meter readings and carefully inspect the area around the meters.


You can protect supply lines and meters from freezing:

  • by providing a sufficiently deep water meter shaft with an insulated cover,
  • by providing additional thermal protection above the meter with insulation materials (thermal insulation cover),
  • with a shaft without bottom, which enables the warmth from the lower layer of the ground to pass directly to the thermal insulation cover,
  • by preventing cool air circulation in the water meter shaft and around plumbing,
  • by providing water circulation through pipes when outdoor thermometers drop into the freezing zone.
     počena vodovodna cev

If you notice any damage to your meter, contact us on ourhotline.

According to the provisions of the Decree on Drinking Water Supply in the area of you municipality, a damaged water meter can only be replaced by a public water service provider. Costs arising from the irresponsible use of water meters are borne by their owners or the users themselves.

The Decree on Drinking Water Supply does not allow the users to disassemble their meters by themselves.

1m3 water costs less than a costly repair of your plumbing.

Bottled water

1. What is the difference between drinking water directly from the tap or from a plastic bottle? What substances does the plastic bottle contain?

The quality of bottled water is, regarding the chemical properties, comparable to the quality of water from a tap. The use of plastic bottles is very practical, but there isn’t any reason why you shouldn’t drink water from the tap, if there is proper drinking water available.

In contrast to tap water, bottled water has been in contact with plastic for a longer period of time. Plastic and other materials which are intended to come into contact with food can release different substances into the food (or water). Plastic materials mostly release organic substances, while other materials like metals, glass and ceramics may release heavy metals. The released substances are residues of starting substances and additives, and also a reaction and decomposition products of the starting substances.  


The release of substances depends on the type of material, type of food (is the released substance soluble in the food), temperature and duration of contact, as well as on the ratio between the volume of the food and the surface of the material. The quantity of the substance that is released into the food is determined by law. The more toxic and the higher the level of the substance present in the environment, the lower the level of permitted amounts in food.


There is no need to be excessively concerned about plastic bottles – when it comes to plastic bottles there is only a very low concentration of substances released (much lower than defined by law). In fact, the concentrations of substances that are released by water bottles are usually below the detection limit of the test methods.


2. What do the different numbers on plastic bottles mean? What types of plastic bottles are there? Is there any difference between them?

The symbol on plastic bottles, a number within a triangle, was developed by the American Society of the Plastics Industry in the 1980s. The symbols provide information regarding the type of plastic the bottle is made from, how biodegradable the plastic is and how to recycle it (however, the symbol cannot guarantee that the bottle will be recycled).

 voda v plastenkah

The symbol 1 within a triangle means that the bottle is made of polyethylene terephthalate (PET), numbers 2 and 4 mean polyethylene (High Density PE (HDPE) and Low Density PE (LDPE)), the number 3 means polyvinylchloride (PVC) and the number 5 means polypropylene (PP), the number 6 means polystyrene (PS) and the number 7 within the triangle means that the product is made of other types of plastic that don’t fit into the other categories, such as plastic resins and polycarbonate. The use of symbols is not obligatory. These symbols don’t offer any information about the release of chemicals into the food and about the safe use of plastic bottles. If the purpose of use isn’t clear, it is much more important for the consumer that there is a symbol of a glass and fork on the product. Material which has yet to come in contact with food can be marked by “intended to come into contact with foodstuffs”, in that way the consumer knows that the product is intended to come into contact with foodstuffs. If the purpose of use is obvious to everyone, for example on coffee cups, cutlery or similar, the symbol isn’t obligatory. The symbol confirms that the product has been made in compliance with regulations for materials intended for contact with foodstuffs.       


Plastic bottles filled with water are mostly made of polyethylene terephthalate – of plastic marked by symbol 1 or PET or PETE. Reusable plastic bottles are mostly produced of tritan (symbol 7) or polyethylene (HDPE and LDPE and symbols 2 and 4) or of polyvinylchloride (PVC, number 3). Water dispenser bottles (in shopping centres, hospitals…) are made of polycarbonate (PC, number 7). Polycarbonate is manufactured with the polymerization of bisphenol A (BPA). BPA is a compound, discussed extensively in the public arena and by the European Commission. The discussed toxicological studies, presented to the Commission, has not provides any reliable proof of the toxicity of BPA which is why polycarbonate plastic isn’t forbidden for the production of materials intended to come into contact with foodstuffs, except for baby bottles. Because children are very sensitive, the European Commission has taken precautionary measures over the use of BPA in the production of baby bottles and has banned their use.


3. Is it important what kind of liquid is in the bottle (for example, is there any difference if there is water or juice contained in the bottle?

 The migration of substances (as you can see in the answer to the first question) is influenced by the type of food.


4. Could the successive use of plastic bottles be dangerous – for example, if you buy a plastic bottle of water and later refill it with water for the following 14 days?

 There isn’t enough information regarding the effect of the reuse of plastic bottles filled with water. The bottles inspected by the manufacturers are only intended for a single use and often stored at room temperature (generally this is the intended use of bottled water). In Slovenia, consumers use them many times due to price and practicality. In the Institute we have already carried out some tests of this type of use – we tested the effect of reusing bottles on the migration of antimony from plastic bottles. For the plastic bottles used by the largest producers of bottled water in Slovenia, we couldn’t find any effect in the repeatedly use bottles at room temperature (the migration of antimony was in all cases under the detection limit of the test methods). We are yet to examine the migration of other substances and the influence of different temperatures during storage.


5. Are different types of plastic bottles safe when in contact with foodstuffs or water?  

Different types of plastic are safe when in contact with foodstuffs, if during their production the manufacturers abide by the special rules that apply. The production process of plastic that is intended to come into the contact with foodstuffs is different from the process of plastic produced for other intentions (plastic floor coverings, plastic pots, wire insulation, and similar). For the production of plastic intended to come into contact with foodstuffs only some special (verified) raw materials can be used (there is a list defined by law). During the production process, producers must handle the materials in accordance with the special rules which apply to materials intended to come into contact with foodstuffs (especially during production). The finished products are then tested and their specific intended use is verified (for specific food, temperatures, surfaces) to ensure that there is no migration of harmful substances or substances which could influence or change the taste, odour or appearance.                                                                                        


In Slovenia, the release of substances from different materials has been regularly and accurately tested for decades. Laboratories are accredited (independent institutions check our work every year and our results are also recognised abroad), they regularly participate in inter-laboratory comparisons with excellent results, as they are familiar all the innovations regarding migrations and their tests, inter alia, they work actively in the European network of reference laboratories for materials that are in contact with foodstuffs. The results presented rarely breach legislation.                                                      


You can find additional information online about the violations and rules imposed on materials intended to come into contact with foodstuffs. The Rapid Alert System for Food and Feed (RASFF) presents a list of disputed samples from the whole of Europe. You can search RASFF using your browser and find all the information you need.  You can also find useful information on the website of the Institute of Public Health of the Republic of Slovenia and of the Ministry of Health. Sometimes, you can find notifications in the media or in shops where the disputed products were sold.


You can always ask experts from the Institute of Public Health of the Republic of Slovenia or from Health Inspectorate of the Republic of Slovenia.


As an interesting detail, here is a comment made by Ms Lučka Kajfež Bogataj, published in the magazine Polet on April 15th 2008 regarding this topic

“Every time you empty a one-litre plastic bottle, you use one quarter of a litre of oil,”

Lučka Kajfež Bogataj

Transport of drinking water

For the transport water you need a stainless steel tanker, used solely for this purpose. Before its use it has to be disinfected with a chlorine solution and then rinsed with safe water or with the water that will be transported.


Water is transported from a water supply system which is safe regarding its microbiological and chemical analyses. Before filling the tank, the water has to be left running for a couple of minutes, because the tank can only be filled with only fresh water. All the materials used for filling the tank must comply with the applicable standards and must be regularly maintained at the highest level of hygiene. Before transportation, the water to be transported must be chlorinated. The concentration of the residual chlorine in the water must be 0.3-0.5mg/l of water.

  prevoz pitne vode


After transportation and after the water had been emptied into the water tank, the level of the residual chlorine must be checked. The concentration of the residual chlorine in the transported water before use must be between 0.3 and 0.5mg/l of water.


The water intended for transportation should be bacteriologically examined more often as part of the internal monitoring in accordance with the HACCP system.


The provision of clean water to every single person and in every place is the basic component of health provisions. In the context of a household or home, the following quantities of drinking water are considered for each person per day:


- A minimum quantity of 20L of drinking water for each person per day is necessary for drinking, cooking and basic personal hygiene – washing hands, washing food, and of which, 7.5L are intended for drinking and cooking.


- Over 50L of drinking water is required for basic laundry and bathing (beside washing, drinking and cooking and basic personal hygiene – washing hands and washing food).


- Over 100L of drinking water is sufficient for additional comfort and well-being.


For the basic physiological needs or to survive – it should be enough to drink on average 2-3L, for children under 10kg it should be 1L.


For food – cooking an additional 2L more of drinking water should be assured for each person per day. This quantity isn’t intended for washing food.


In the context of the provision of a minimum quantity of drinking water (drinking and cooking) a number of things need to be taken into consideration: firstly there should be the climatic conditions, physical activity, gender, age, some physiological conditions (pregnancy, breast-feeding), nutrition and health conditions. If one considers the needs of breast-feeding mothers with moderate physical activity in temperate climates, the necessary quantity of drinking water would be around 7.5L a day (to drink and to cook). This quantity should be enough for most people in most conditions.                        


In exceptional situations the minimum quantity of 7.5L of drinking water should be provided for one person per day. In such conditions the efficient use of a minimum quantity of 7.5L should be also established for basic personal hygiene. Such a supply can last only 2-3 days. Further on, the quantity should be increased to at least 20L per person per day, exceptionally to 15L for one person per day.

If the drinking water is transported to the users, the minimum quantity of drinking water should be provided for each person.

Drinking water preparation

What does drinking water preparation mean?

The preparation of drinking water (other expressions are also used: cleaning, conditioning, treatment) signifies the treatment of water to ensure compliance with drinking water health regulations. Often, this is the only way to provide drinking water because environmental pollution is getting worse and worse; new requirements appear and the quantity of water is limited, as the water resources themselves are becoming more limited. In Slovenia, for the supply of drinking water, water that doesn’t need preparation is the preferred option.


What kind of preparations are there?

For preparing drinking water, physical, chemical and biological methods are used, alone or in combination with others. Preparation can be complete or partial; it can be limited with regard to its disinfection. The probability and the consequences of microbiological pollution of drinking water demand taking measures that put priority in this area or to ensure that the pollution with disinfection by-products are minimised as much as possible, without threatening the effectiveness of the disinfection.


How to select the right way of preparation?

The right way of preparation has to be selected for each single supply in accordance with an evaluation of the area, the features of the drinking water catchment, and repeated laboratory tests of the untreated water quality and the state of other elements within the system. We have to be aware of specific, realistic and potential pollutions. The preparation depends on the degree of water cleanliness we’d like to reach and on the type of pollution.


What approach offers the best results for supply?

The approach of multiple barriers includes the selection of the best available resources, its protection and safety, optimal preparation and a perfect water network. The preparation includes at least the disinfection and eventual filtration of all waters (except high quality primary resources). The use of multiple barriers provides an adequate level of safety also in the event of the failure of a single element.


What has to be considered, when deciding to prepare the drinking water?

Preparation should provide a great enough reserve in the event of repairs, maintenance or the failure of a single component. If disinfection has to be done, the entire emergency setup has to be double. The efficiency of the preparation depends on the operation of the facilities – sometimes they don’t work as promised by the manufacturer, sometimes they are not adapted or they aren’t well maintained. The operation of the installed facilities should be tested and the previous experience has to be taken into account. For optimal results, a qualified operational team for work within the facility is necessary.


What about dilution of the water?

Sometimes water dilution or mixing the water of different qualities can also be part of water preparation. Water dilution must be used exceptionally and only for a transitional period; the right approach is the elimination of the cause of the pollution and not only to keep the value below the permissible level.


What procedures can be used for preparing drinking water?

The following procedures can be used in the preparation of drinking water:


- Distillation

This method is used for the desalination of sea water or when we want to separate the volatile substances or solids that remain. We can get very clear water where there could be volatile chemicals present.

- Aeration

By using aeration, gases are changed – the oxygen input and the elimination of sulphuric hydrogen, carbon dioxide, radon, etc. This type of process can be effective using iron oxidation or manganese oxidation or the elimination of odour and taste.

- Coagulation

Particles including microorganisms are combines into bigger flakes which settle faster. This process can be accelerated by adding agents – coagulators, like aluminium sulphate or ferric chloride or synthetic polymers. The flakes are removed by sedimentation or/and filtration. With this procedure we can reduce the number of microbes by 90-99%.

- Flocculation

Slow mixing that increases the contact between the particles and the flakes and the union into bigger flakes is made easier. The process is combined with coagulation.

- Sedimentation or precipitation

Because of gravitation, the particles precipitate, including the microorganisms. This process is slow and any movement can slow it down. Sedimentation is improved by adding a coagulant. The sediment or sludge is the waste which contains a lot of water that has to be removed. We can dry it, and use a filter press or a vacuum.

- Filtration

When pouring water through a porous structure, small particles adhere and settlePri pretakanju vode skozi porozne strukture pride v porah do adhezije in sedimentacije drobnih delcev, vključno mikroorganizmov., as do the microorganisms. In general, it is a mechanical catching where the dimensions of the stopped particles are much smaller than the size of the pores. Sometimes chemical reactions and biological processes take place in the pores.


What is a sand filter?    

Sometimes the filter is known as the rapid sand filter. The thickness of the normal sand filter layer is 1m, and the sand granulation in the layer is 0.5 – 1mm. The surface under the filter layer must be well drained, the water shouldn’t stagnate, and it must be equipped with a leaching nozzle. Cleaning is necessary when the filter is full and permeability is reduced. When the counterstream is switched on, the sand goes up and when the counterstream is switched off it goes down.


What is direct filtration?

It is the procedure of filtration without an added coagulant if it isn’t necessary because the untreated water is relative clean.


What is a slow filter?

It is also called a biological or English filter. In some cases, a biological membrane grows on the surface of the filters and helps to remove particles, and the degradable organic substances decompose within the membrane. The filter needs to be much larger and with smaller granulations. It is very efficient and simple to run. When the permeability is reduced, the upper layer is removed mechanically and then the filter needs time to mature, which means that the biological membrane grows again. In this kind of filtration no coagulants need to be added.      


What is a diatomaceous filter?  

Using the filters of diatomaceous earth (the fossilized remains of tiny aquatic organisms) water is mixed with the diatomaceous earth and pushed it onto the membrane using a stream of water or we load it on the membrane where the filter layer is built. The filters get blocked (that’s the reason why they are not suitable to the use with coagulants) and they are often broken through because the accumulated filter layers are thin.


What is membrane filtration?

Separation using membranes with cleaning liquids or gasesLočevanje z membranami pri čiščenju tekočin ali plinov ni nov postopek isn’t a new procedure. The filtration membranes can be divided according to the size of the pores. Ultrafiltration stops viruses, bacteria, and the biggest molecules while the disinfection method is reliable enough. Larger pores and bigger permeability have microfilters, while the pores used in nanofiltrationpore so pri nanofiltraciji manjše are smaller and in reverse osmosis still smaller. By using reverse osmosis, the dissolved solid particles, ions and molecules are separated using the semi-permeable membrane and pressure.  


What kind of filters are there?

In microbiological laboratories, the physical elimination of microbes is known as the disinfection method or even sterilisation; classic examples are ceramic or porcelain (Chamberland’s) filters or filters of fine pressed diatomaceous earth (Barkefeld), while Seitz filters are of plaited asbestos fibre. Different combinations with other cleaning procedures are also possible.


What is adsorption?

Usually, special specific adsorption means are used, for example activated carbon, which can be in granular form (granulated), G-filter, and P-additive in powder form. They can be used to remove the odour, taste and a lot of organic chemicals, also chlorinated products and radon. The carbon can be from bone, wood or coal. The activated carbon has small pores, and its adsorption capacity increases. Biologically activated carbon is the activated carbon on which microorganisms grow and by which biological cleaning mechanisms, in comparison to adsorption mechanisms, become more important.


What is ion exchange?

Ion exchange is the most commonly used technology for the elimination of ions that cause water hardness. In the drinking water from taps, a specific quantity of salt is dissolved. It is visible when the water boils and at the bottom of the pot remains a white powder (boiler incrustation). The ion exchanger removes it physically and protects the pipes of the water network and devices connected to the network. It ensures easier cleaning and a lower consumption of detergents.


Water preparation is the treatment of water to provide health compliance of water.

The preparation of drinking water (other expressions are also used: cleaning, conditioning, treatment) signifies the treatment of water to ensure compliance with drinking water health regulations.

Disinfection of drinking water

Disinfection of drinking water is the process during which harmful microorganisms are destroyed. By disinfecting drinking water infectious diseases caused by microorganisms in the water are eliminated. This is why disinfection is a mostly indispensable process for the preparation of drinking water.  


How is drinking water disinfected?

Various chemical substances are generally used for drinking water disinfection: chlorine gas, hypochlorite compounds, chlorine dioxide, ozone and physical procedures, like UV-radiation, ultrafiltration and boiling.


How is disinfection categorised regarding its place of activity?

The disinfection process can be categorised in view of the place of activity, primary and secondary disinfection. Primary disinfection destroys the microorganisms in the untreated water, which cause diseases, and it takes place during the preparation on the spot of water preparation. Secondary disinfection prevents the growth of bacteria and protects the water against additional pollution in the network. It can be called residual disinfection and it takes place in the distribution system. Disinfection agents used in those procedures can be different. The primary disinfection procedure usually provides a residual effect at the same time.


How does the disinfection agent work?

The disinfection agent:

- destroys all microorganisms (bacteria, viruses, protozoa) in different conditions and in an acceptable time,

- shouldn’t be toxic or irritating for people or animals,

- should be cheap, safe and easy to use and handle,

- provide residual functions and offers easy handling.


Is disinfected water harmful to your health?

Disinfection agents don’t only react with microorganisms but also with other ingredients in water, and during those reactions could some new substances may be produced – by-products of disinfection which may be harmful to health. After chlorination for example, trihalomethanes are produced.


How does the ozone work?

Besides disinfection, the ozone oxidizes oxidable inorganic substances; it removes colour, odour and taste. It doesn’t work residually and it can be secondarily combined with chlorination. After ozonisation, many new compounds may be produced, some of them are mutagenic or carcinogenic. If there is bromide in the water treated using ozone, bromate will be produced.


What must be provided by an operator if they do not carry out water disinfection?

If the origin and the certified quality of the drinking water ensure that microbiological pollution isn’t present, if the network is safe, the flow is constant, the consumers are within a short reach, then disinfection can be neglected. This is then be proved by the monitoring; it means the constant health compliance and safety of supply, including ecological and epidemiological safety.      


By disinfecting the drinking water, we prevent infectious diseases caused by microorganisms in the water.

By disinfecting drinking water infectious diseases caused by microorganisms in the water are eliminated.

Conditions for carrying out disinfection of water network

Disinfection must be ordered at least five days prior to the actual disinfection.

  1. The building is built. All taps and outflows must be connected.

  2. The water network must be constructed so that the disinfection agent can be added in one place or if necessary in more different places (a valve and a T-piece is installed under the water meter). The water network shouldn’t have any blind pipes.

  3. A water network pressure test must be done.

  4. The water network shall be well cleaned out before disinfection. It must be washed so that clear water flows from all sinks (organoleptically clear, visually clear water without any odour).

  5. Before chlorination, the customer has to allow the operator to examine and revise the water and hydrant installation or revise the operational plans.

  6. During disinfection, the responsible implementer of the water network must also be present, who know all the details of the situation and has carried out work on the water and hydrant network.

  7. During disinfection, the water shall not be used, the disinfection operator must provide a written warning about the prohibition of water use.

  8. The disinfection lasts a minimum of three hours in smaller buildings, in other buildings 12-24 hours; the concentration of the disinfection agent is 5-10 mg Cl2/L.

  9. The number of samples that need to been taken: smaller buildings (only samples for bacteriological tests of drinking water need to be taken, the number of samples is a maximum of 1/3 of sinks (taps)); other buildings (bigger networks for supply of settlements, streets or parts of streets, bigger complexes of flats, hospitals, health centres, schools, kindergartens, hotels, larger restaurants with kitchens): samples need to be taken twice, the first time for the bacteriological examination and for the analysis of mineral oils, the second time for bacteriological examination and chemical analysis.

  10. During the sampling, a so-called control sample of drinking water must be taken from the network; before water installation so that we can disinfect it, if possible. The control sample is taken to compare it to those water networks, where the drinking water was often unfit for use. The disinfection is considered successful if the bacteriological results of drinking water samples, taken from the water network after the disinfection, were good or as contaminated as the control sample.

  11. The certificate on disinfection is issued after the end of the examination of the last drinking water samples (the minimal necessary time for the bacteriological and chemical analysis of drinking water).


If requirements 1-7 are not fulfilled, the disinfection of the water network cannot be done.

During disinfection, the water shall not be used.


Chlorination is the most commonly used procedure of disinfection. Chlorine destroys bacteria and some viruses; however, in the quantities usually used, it doesn’t destroy parasites. The water should be in contact with the chlorine for at least 30 minutes. After reacting, it should keep some free remaining (residual) chlorine. The concentration of free remaining (residual) chlorine in the water network should, after the completed disinfection, be between 0.3 and 0.5 mg/L, it may be lower if the operator in view of the circumstances can assure the constant microbiological compliance of the drinking water. From the point of view of the WHO, the calculated sanitary value of the free remaining chlorine is 0.5 mg/L of water.


What is hyperchlorination?

Hyperchlorination (also chlorine shock) is a form of disinfection of water or water supply network elements (pipes, tanks …). We decide to carry out hyperchlorination following the similar criterion as forboiling water. We implement the hyperchlorination of the network to prevent or eliminate non-compliance of drinking water which comes from the network, for example after maintenance work, sanitation or pollution. In this procedure we use a higher concentration of the chlorine agent as in the usual chlorination; often the concentration is ten times higher (over 5 mg/L). During hyperchlorination it is forbidden to use the water from the network.      


What is contact time?

If we want to destroy microorganism during the primary disinfection, we have to provide the right concentration of the disinfection agent – C (mg/L) and the right reaction time – t (min); this is the contact time (C.t). If the concentration of disinfection agent is higher, the contact time can be shorter. We can provide the contact time in the tank or in the network.


What is water dechlorination?  

If the quantity of residual chlorine is too high, it has to be removed. The procedure is called dechlorination and we can do it with aeration, adsorption using activated carbon or with chemical substances. We usually use sodium thiosulphate or sulphur dioxide.


Why is it important to control residual or free remaining chlorine?

In the event of subsequent water pollution, the residual disinfection agent reacts (if we talk about chlorination, this is the free remaining chlorine) with contaminants and in this way it is used up. We cannot prove the residual chlorine in the water or there are lower quantities of the residual chlorine. The control of residual ensures the control of information about water safety.


How can chlorine be detected in the water?

To determine the concentration of free remaining chlorine in the water a method is used where we first add the reagent DPD to the water. It can be in the form of pills or liquid. The reagent DPD colours the complex in red after reaction with chlorine. The method is suitable for determining the chlorine in the water in concentrations of 0.1 to 6.0 mg/L.


Is the water in Slovenia chlorinated?

In Slovenia, the disinfection or chlorination of drinking water isn’t provided for by legislation. The need of disinfection and its means of implementation are determined by the operator of the system for each individual single means of supply. The operator has to ensure the compliance of drinking water, and the same applies for undesirable substances present after chlorination.


How can you know that your drinking water has been chlorinated?

For any information about disinfection or chlorination you can ask your drinking water supply system operator. The amount of chlorine in drinking water that makes it no longer odourless is ca. 0.6 mg/L, some people can smell it in the concentration of 0.2 mg/L. It is more intense in warm water. If drinking water smells of chlorine, it is does not represent a non-compliance.


What does it mean if water smells of chlorine in an unknown place?

It means that, most probably, the water is much safer for use than water without this smell.


Can you use iodine to disinfect drinking water?

In emergencies or when travelling you can use iodine. It destroys the majority of pathogenic microorganisms, however to eliminate Gardia cyst you need more time; the iodine is not efficient against cryptosporidium. We don’t recommend iodine for water disinfection for children, pregnant women, people suffering from thyroid diseases and people allergic to iodine, except in cases when after disinfection the iodine will be removed, for example with activated carbonate. You can taste the iodine in the water in concentration of ca. 0.15 mg/L. A drinking water disinfection agent can be in four different forms: iodine tincture (2 % solution – use 5 droplets/L), iodine (10 % solution), iodine pills and iodine resin (triiodide, pentaiodide). The disinfection is carried out according to the manufacturer’s instruction; if the water has a temperature of 25 °C it should last at least 30 minutes, longer if the water temperature is lower.


Why is iodine so important?

Iodine is an essential element, necessary for the thyroid hormone. If we consume too much iodine we can become ill with hypothyreosis (an underactive thyroid) or hyperthyreosis (an overactive thyroid). Hypersensitivity reactions or poisoning are also possible. The defined value for iodine in drinking water isn’t determined, so warnings against the use of iodine for drinking water disinfection agent are necessary.

Chlorination is the most commonly used procedure for disinfection; chlorine destroys bacteria and some viruses.

The acidity of water

The acidity of water can be defined very easily. You can use a test strip that can be bought in shops. Put the strip into a sample of water. The strip changes colour and using the colour code you can determine the acidity level according to the pH-value. Water with a pH of 7 is neutral. When the pH is less than 7, it is acidic and when the pH is more than 7, it is alkaline. Alkaline water is strong antioxidant which removes free radicals from the body and neutralises very harmful oxidants.      

 Ugotavljanje pH vode

Body acidification is reduced and the first defence line of our health becomes more successful. Because of two times smaller clusters (groups) of water molecules than in tap water, hydration of the body is faster and more intense, tea, drinks and food taste significantly better.


    • Drinking alkaline water is the best protection against carcinogenic diseases.

    • It reduces the blood sugar level and reduces blood pressure.

    • It protects against osteoporosis.

    • It alleviates cardiovascular diseases and detoxifies the body.


Acidic water, which is the by-product of ionisation, can be used as excellent natural sterilizer for cleaning, hygiene, food conservation, oral hygiene, face, skin and hair care.  


The quality of water is influenced by its acidity. We measure the acidity of water with a negative logarithm of hydrogen ion concentration. The ion concentration is expressed with pH; the acidity is greater the lower the pH value.

 Source: eRevija

Alkaline water is a powerful antioxidant which removes free radicals from the body and neutralises very harmful oxidants.

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