Urbanization during last centuries has led to growth of the cities worldwide and centralized drinking water supply system (DWSS) is vital to ensure healthy and evolving society. The aim of DWSS is to supply clean and safe drinking water to every point of the DWSS. The drinking water must satisfy chemical, biological and aesthetic requirements included in legislation of every state or country. In most of the cases drinking water quality meets the requirements straight after the treatment. However there are numerous cases when consumers have got sick by using poor quality drinking water. Pipe breaks, bacterial regrowth, maintenance and construction works of DWSS, corrosion of pipelines, sewerage cross connections, failure of water purification plant, deliberate drinking water contamination might cause water quality deterioration at the consumption point (Lee et al., 2012). Although the legislation in modern countries says that random “grab” samples must be taken to monitor the drinking water quality, the continuous monitoring of drinking water quality is essential to deliver safe water to consumer. Moreover, conventional microbiology testing methods can take several hours or days, which would lead to long response time of water authorities in case of contamination. That is the reason why the on-line monitoring of drinking water gets more popular in most developed countries. The use of on-line monitoring can reduce response time to several minutes or even seconds. The aim of this study was to investigate the ability of on-line sensors to detect the daily fluctuations of drinking water quality and impact of extended internal water network on drinking water quality.