Drinking water for the Riga city is provided by the groundwater well field “Baltezers, Zakumuiza, Rembergi” and by the Daugava river as a surface water source. Presently (2016), they both supply 122 thous.m3/day and they do not exploit ever a half of their power. Therefore, it seems reasonable in future, to use only groundwater, because water of a river is of low quality and its treatment is expensive. Scientists of Riga Technical university by using hydrogeological model of the well field “Baltezers, Zakumuiza, Rembergi” have proved that its capacity covers demand (120-122 thous.m3/day of drinking water for Riga in 2030. Therefore, it is possible not to exploit the Daugava river as the water source. The research was done as the task drawn up by the company ”Aqua-Brambis”. The company asked to evaluate hydrogeological properties of several versions of water supply of the Riga city. It was necessary to check stability of syphon type systems that extracts groundwater for the city under conditions of their increased productivity. It was also proved that the syphons may be replaced by a pumping station. Then the number of exploitation wells considerably decreases. The impact of expenses related to reconstruction of the wellfield and the water distribution network is not considered. The publication may be of interest for specialists dealing with problems of water supply for large towns. Keywords: hydrogeological model, groundwater well fields, syphon, pumping of groundwater.