The sources of groundwater are mainly river water from the Vosso, which infiltrates into the loose sediments from the river along the east side of the forested Prestegardsmoen. A little of the groundwater comes in addition from rain and snow that falls directly onto the fine sand. After the water level in Lake Vangsvatnet was lowered permanently in 1991, no more ground water infiltrated from Vangsvatnet. Water particles take about 60 days to get to the Vosso pumping wells, the nearest of which lies 100 metres from the river bank. There are four pumping wells in operation. The first is from 1972, but this was replaced with a new one in the late 1980s. The water is pumped into the well pipe 20-24 metres under the surface.
The water quality of the groundwater from Prestegardsmoen is very good. The water is essentially lacking in bacteria and has an acceptable mineral content and temperature. The somewhat low pH and oxygen levels get adjusted by filtering the water through a marble filter and by aerating the water. Consumption of water has gone down in recent years, mainly because the pipeline network has been modernized and repaired. In 1997, the consumption was about 90 litres per second on average throughout the day; in 1998 this fell to about 60 litres per second, varying a bit throughout the year.
In order to protect Prestegardsmoen as a reliable water source also in the future, the municipality has divided the area into distribution bases with strict restrictions on all activities that might lead to contamination of the groundwater.
