What water

Description of the characteristic indicator parameters in potable water


The potable water in Sofia has a low content of dissolved solids, which makes it suitable for everyday use and useful for the normal functioning of the cells in the body.

The average value for the indicator Total Hardness in the water supply system of Sofia City is < 0.89 mgeq/l or less than 2.49 dH (German degrees), which categorizes it as ‘soft water’.

The potable water is supplied mainly from Rila Mountain water sources that are collected in Iskar Dam and Beli Iskar Dam.


The average value for the indicator Total Hardness in the water supply system of Sofia City is < 0.89 mgeq/l or less than 2.49 dH (German degrees), which categorizes it as ‘soft water’.

Active reaction (рН) – indicator determining acidity or alkalinity of water.

Electrical conductivity – determines the amount of dissolved salts in the water.

Taste, odor and color – water for potable and domestic needs is tasteless, odorless and colorless. The presence of taste, odor and color is caused by dissolved salts, minerals and gases in the water.

Turbidity – an indicator of reduced transparency of potable water. It is caused by the presence of mechanical impurities and/or development of plankton in the water.

Total hardness – the hardness of water is determined by the presence of minerals solved in it (salts of calcium, magnesium, strontium and barium).

Free residual chlorine an indicator determining the part of chlorine added for treatment which is free to deactivate the disease-causing organisms and is used for continuous disinfection. The quantity of free chlorine in potable water is such as to ensure effective water disinfection, on the one hand, and, on the other hand, to not exceed the threshold of 0.40 mg/l. Chlorine is a biocide that destroys the microflora in water and in some cases has a positive impact on other indicators such as color and turbidity. It is very important for potable water to be disinfected and not contain disease-causing bacteria, viruses and parasites that cause gastro-intestinal infections and more serious diseases. It is quite normal and in line with the recommendations of the World Health Organization that after performed disinfection a small quantity of ‘free chlorine’ to remain in the water to the tap of customers. This ensures prevention of the development of harmful bacteria in the entire water supply network.

When the water in the glass is white colored it is caused by air bubbles contained inside. After a few seconds the bubbles pass in the air. The comprehension that the “white water” is over chlorinated is wrong!

Ammonium ions, nitrates, nitrites – indicate changes in time of the water quality due to specific impurities found in these compounds.

Aluminum is naturally found in water and it results from the treatment process for obtaining potable water

Iron – the sources of iron are usually natural - minerals or from the installation of the water supply network. Iron is a natural component of the water.

Phosphates an indicator determining the presence of phosphate ions in water. Phosphates are not toxic to humans unless they are present in extremely high concentrations.

Fluorides – sources of fluorine can be minerals, soils and industrial pollution. They are not hazardous for human health if their values are low. Fluoride is not used for disinfection of potable water in the area of Sofia. The potable water in Sofia contains about 0,07 mg/l Fluorides. That is 20 times less than the permissible value.

Radiological indicators (alpha activity, beta activity, indicative dose, tritium, uranium, radon) - sources of radiation may be minerals/ores containing radioactive elements which emit radiation upon their decomposition.

Radon has included in the Regulation 9 and controlled since 28/11/2015.

Uranium has controlled as a chemical element (not radiological) since 28/11/2015.

In potable water in Sofia Radioactive substances are not detected.

Coliform bacteria and Escherichia coli Coliform bacteria are usually present in the environment and the gastro-intestinal system of animals and humans. They are the most common indicator of the bacteriological condition of water. They are destroyed in the process of disinfection of potable water.

Clostridium perfringens – the presence of these bacteria in potable water shows fecal contamination. These bacteria are not found in potable water.

The water in Sofia does not contain lead, mercury, arsenic and pesticides.

The presence of the indicators above in the water does not represent a risk unless they exceed parametric values, determined in the regulations.


In connection with the Regulation 9/ 16.03.2001 Sofia Water Company provide actual information about the quality of drinking water, expressed in annual and monthly reports.

The annual report contains the average annual values for the indicators ‘total hardness’, pesticides (total), lead, arsenic, mercury, fluoride, phosphates as well as radiological indicators such as uranium, radon, tritium, indicative dose, total alpha and beta activity for the last calendar year during which the tests were conducted. The data are presented in two separate tables – one for the physicochemical indicators and one for the radiological indicators and contains also measurement unit, average annual value and admissible value. The selected indicators are a part of the periodical monitoring as per Ordinance 9. The frequency of the periodical monitoring is lower than the frequency of the continuous monitoring. It is legally set and is different for each point and depends on the water supply volume to the relevant region. This type of reports is published once a year. In case that monitoring was not executed by the periodical indicators for a given point in a given year, the report shall be published or renewed immediately after its conduct. The data contained in these reports reflect water quality for a period of one year in a specific control point.

The monthly report contains data for pH, electric conductivity, free chloride, aluminum, iron, manganese, ammonium ions, nitrates, nitrites, turbidity, color, taste, odor as well as microbiological indicators - Clostridium perfringens, coliform bacteria and E. coli. The data are presented in two separate tables – one for the physicochemical indicators and one for the microbiological indicators and contains also measurement unit, calculated result from the analysis and admissible value. In the report there is information about the address of the control point, the date of sample taking and identification code of the sample. The selected indicators are a part of the periodical monitoring as per Ordinance 9. The frequency of the continuous monitoring is higher than the frequency of the regular monitoring. It is legally set and is different for each point and depends on the supplied water volume to the relevant region. This type of reports is published every month, when monitoring is executed for a given control point. The data contained in these reports reflect the actual water quality at a specific moment of sample taking in a specific control point.



The quality of potable water, supplied by SV for the entire concession area (Municipality of Sofia) is determined in compliance with the requirements of Ordinance No 9 /16.03.2001, last amended on 12 December 2014.


  • The points for sample taking are specified jointly by Sofiyska Voda JSC and the Regional Health Inspectorate in Sofia and are 86 nos.
  • The frequency of sample taking and analysis of each control point in Sofia and the region are determined depending of the water volumes supplied to it in compliance with the requirements of Ordinance No 9. That is why; each control point has different frequency of the control.
  • The admissible values of the tested indicators are stated in Ordinance 9/2011 for the properties of water, designated for potable and domestic purposes and are the threshold up to which the components contained in water do not pose a danger on human health.
  • Sample taking is executed in accordance with established international standards and by trained specialists.
  • The analyses of the samples are carried out using accredited methods – established international standard and inter-laboratory methods.
  • On an annual basis SV takes about 2,000 control samples from the control points on the water supply network at the consumers’ and about 40,000 analyses are made. The number exceeds the minimum statutory required number of control samples with about 20%.
  • Every day, team of 30 qualified and trained specialists – biologists and chemists is care for the control of potable water indexes. Laboratory Testing Complex has accredited according to the ISO 17025 since the beginning of the 2010.
  • The potable water control is constant. Samples are taken every day, also during the weekend and holidays.



Make sure that you have drained sufficient volume of water. Draining should last 2-3 minutes to establish a constant water temperature after the rotation of the valve. If the problem continues to exist after the draining, send a signal to us online by the website or on phone 0700 1 21 21.

After the receipt of your signal, we will make an inspection of the condition of the water supply network in the area and if it needed inspection of the quality of the supplied potable water. If a problem is ascertained, we will take corrective actions. If you request for feedback, we will keep you informed.

The undertaken corrective actions include flushing water mains and refreshing the water in the risky sections of the network. An annual program is implemented for mechanical treatment and disinfection of all service reservoirs and facilities on the way of water in Bistritsa PWTP and Pancharevo PWTP. The long-term measures include implementation of investment projects for renewal of water mains and/ or water service connections.

Potable water quality in Sofia is comparatively stable. Despite it the keeping of stable indicators is a dynamic and continuous process.

In some cases deviations in the water quality may occur after emergency or planned braking of water supply. In most cases our observations shows that the deviations are due to the outdated domestic water services connections, maintenance of which is outside the responsibility of the Water operator.