Introduction. The Virttaankangas glaciofluvial/glaciolacustrine complex is part of the largest esker system in southwestern Finland (Fig. 1). A plan has been prepared for the area that will involve the production of an artificial groundwater reserve from infiltrated river water for the use by the city of Turku and its surrounding area. The amount of river water infiltrated into the esker aquifer will be about 1.3 m s. This is about 0.5 % of the mean flow of the River Kokemäenjoki, which will be the initial source of the water (Jaakko Pöyry Infra 2001). The artificially infiltrated groundwater will be supplied to 285,000 inhabitants of the Turku area in the beginning of the year 2007.