The ground and spring water reserves used by the Landeswasserversorgung are fed from the karstified Jura mountains of the Swabian Alb region. Because of the long period for which the water is underground, the seeping precipitation water absorbs many minerals and particularly limestone on its way. The groundwater transported in Donauried naturally displays an average total hardness of 22 degrees of German hardness; the average values in Egau waterworks are 18.5 degrees of German hardness.

A large proportion of the drinking water delivered is used as service water. The water hardness plays a major role here in the heating of the water, due to the mostly undesirable deposit processes, or in the measuring of detergents. To satisfy the desire for softer water and benefit from the economic and ecological advantages of central drinking water softening, Langenau waterworks has a central decarbonisation plant. It is therefore possible to deliver the groundwater extracted from Donauried to the customers as drinking water at 13.0°dH (hardness range average). After the positive experiences at Langenau waterworks, a decarbonisation plant was also constructed at Egau waterworks. There, the karst spring water is softened to 13.0°dH.