On selection of threshold values in alarm-systems for drinking water monitoring / Om val av larmvärde vid dricksvattenkontroll i realtid
During a one year long research project at Borensberg Waterworks, Motala, Sweden, water quality with respect to microscopic particle counts both in raw water and drinking water have been monitored by an online water quality monitoring system. Microscopic particle counts were documented with absolute values in real-time. In this paper, a discussion is introduced on how to analyze large data sets from this kind of monitoring and how to assess threshold values in practice for particle counts in water samples. Statistical tools were used for data sorting and arrangement. Log Reduction is used for comparison of two water qualities and visualization of the treatment process within the waterworks. Numerical analysis of GEV (Generalized Extreme Value) followed by recurrence curve analysis is suggested to be applied for threshold value definition. Results from threshold value definition show that the starting value should be determined by a combination of the theoretical analysis and the practical situation. A calibration of values for specific waterworks should be taken into account when choosing relevant threshold values for water quality monitoring.