The Tallkrogen water service reservoir is part of Stockholm Waters water distribution system. The service reservoir consists of two circular tanks. It has a total number of 35 100 m³. During the period of September 4th to 13th, the Tallkrogen water service reservoir was cleaned from deposits on the bottom. The work was done by WEDA Water using a WEDA VR-600. The reservoir was in full operation during the cleaning process.

Water quality samples of outgoing water were taken from the tank during the cleaning process. Chemical and microbiological analysis showed that the water quality was normal and well below limits. (See table in Chart A, where all analysis are reported

An online turbidity meter measured the incoming/outgoing water to/from the tank undergoing cleaning continuously. To get a complete view, the turbidity was measured before, during and after the cleaning period. The idea was to see if the cleaning process caused a difference in water quality between the incoming and outgoing water. The turbidity however was low all the time, less than 0,10 FNU. The difference between incoming water during the night and outgoing water during the day could be noticed only as a very low "noice" in the curve. The results from the online turbidity measurements are reported in a diagram in Chart A. The peak of 0,09 FNU on the 12th of September is still very low and of no practical importance. Cleaning of the area around the inlet/outlet or the opening of a valve to the second reservoir probably caused this low peak.

The investigation shows that the WEDA VR-600 system in our case allows the water reservoir to be in operation during the cleaning process while maintaining good water quality.