| Summary: | Risk-based sampling program of microorganisms in the water source in northern Sweden After several disease outbreaks caused by parasites in the drinking water during the last years, it is more essential than ever to insure that the water supply companies have enough barriers to counteract the presence of microorganisms in the outgoing water. It is also discussed whether climate changes such as increased precipitation can have a connection to the increased cases of parasites in water sources. The water source at Gäddvik is Luleå municipality’s largest and provides drinking water to 64 500 of Luleå’s 74 000 inhabitants. The investigation of microorganisms in the water source, especially in the Lule River has not been as prioritized as the sampling of chemical parameters. Therefore a risk-based sampling program of microorganisms has been established. After analyzing former tests both on the Lule River and the wells at the water supply companies, and observing the precipitation variability over the last 40 years, a sampling program was developed. Analyzes of the chemical parameters from the river have not revealed any significant changes during the sampling time. The precipitation has shown an increasing trend over the past 40 years. The sampling program was divided into three groups containing the parasites Cryptosporidium and Giardia, some indicator organisms (Escherichia coli, coliforms and Clostridium perfringens) and phytoplankton. The infiltration time during the artificial recharge is too short and therefore it is necessary to expand the Standard control for microorganism in the wells (from 12 to 24 samples). The sampling frequency for parasites should be higher during days with heavily rainfall and during the spring flood.
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