In 1997, 204 236 analyses of specified water quality indicators in a total number of 13 794 samples taken from 3 090 sampling sites of distribution network were carried out by VaK laboratories.
No significant changes between years 1996 and 1997 occurred in the quality standard of drinking water produced and supplied to consumers by VaK . Percentage of drinking water samples not complying with the STN 75 71111 Standard ‘Drinking Water ‘ did not exceed the level of 5 % (in 1995 it was 4.51% and in 1996 - 4.54%).Indicators most considerably contributing to this percentage were identical to those of previous years and their limit values are specified in the above mentioned standard. The indicators with the highest limit value occurred only in the minimal number of cases and indicators with limit value of acceptable risk were not present at all.

Epidemiological Safety Indicators

In order to safeguard the purity of drinking water microbiological and biological indicators of water quality must be regularly monitored. Problem-causing indicators in 1997 were:

• cesspit (thermotollerant) coliform bacteria
• coliform bacteria
• enterococcus (cesspit streptococcus)
• psychophilic and mesophilic bacteria
• living organisms.

Source: VUVH
 
 

Chemical Safety Indicators

With reference to inorganic water quality indicators in 1997, limit values of the following indicators were most frequently exceeded: nitrates, manganese, iron, ammonium ions, nitrites. To a lesser extent drinking water pH and COD_Mn caused problems.
 

Drinking water inorganic quality indicators - the results of analyses carried out in 1997 (SR)
 

Indicator	Number of analyses		% of analyses complying with STN standard
	1996	1997	1996	1997
Nitrates	10 178	8 816	99.29	99.07
Manganese	8 263	6 770	99.38	99.08
Iron	8 571	9 188	96.0	97.94
Ammonium ions	9 902	8 599	99.75	99.74
Nitrites	10 062	10 300	99.53	99.74
Water pH	-	9 026	-	97.08
CODMn	10 391	10 568	99.80	99.82

Source: VÚVH
 

With regard to drinking water quality organic indicators, limit values specified in STN were not exceeded, however, the frequency of their determination is significantly lower than it is with inorganic substances.
Within the group of radiological safety indicators total bulk activity Alpha and bulk activity of Radon 222 were analysed . Total bulk activity Beta did not exceed limit values.
 

Drinking water radiological safety indicators - results of analyses in 1997 (SR)
 

Indicator	Number of analyses	% of analyses complying with STN standard
Total bulk activity Alpha	186	95.16
Bulk activity of Radon 222	167	89.82

Source: VÚVH
 

Disinfection

Chlorinating is currently the dominating method of disinfection. Limit value for active chlorine content present in treated water is 0.3 mg per l. In distribution network the minimal value of active chlorine should be 0.05 mg per l.
In 1997, the percentage of non-compliant samples regarding the active chlorine content varied from 12 to 42%. Majority of analysed samples contained less than 0.05 mg per l of active chlorine or the presence of active chlorine was not detected at all. These values concern samples taken from the distribution network.
Despite the fact that almost 40% of analysed samples taken from the distribution network contained less active chlorine than required, microbiological water quality complied with STN.