Protection of ground water is a major priority of the City of Lahti, because Lahti is situated near to one of Finland's largest areas of ground water, formed by Salpausselkä and the longitudinal ridges joined to it. Most of the area of the city belongs to a ground water region classed by the environmental authorities as important, and all the water used in Lahti is ground water.

All the mains water in Lahti is ground water, and the city is nationally famous for the good quality of its water. Lahti has seven ground-water pumping stations: Jalkaranta, the Sports Centre, Renkomäki, Riihelä, Kärpänen, Laune and Kunnas. For the needs of the city, these stations annually pump more than 8 million cubic metres of ground water, which averages about 23 million litres per day.

A map of Lahti's area of ground water 
Pohjavesialue = groundwater area
Phjaveden muodostumisalue = formation area