Abstract The groundwaters of major karst springs and several piezometers and wells in the Damascus limestone aquifer systems (Syria) have been investigated using chemical and environmental isotope techniques. The groundwater bodies of major karst springs mainly originate from direct infiltration of atmospheric water. The groundwaters emerging from the Figeh main spring have lower stable isotope concentrations than those emerging from the Barada spring. Stable isotopes show that the elevation of the recharge zones of the Figeh main spring (1750 m above sea level) is higher than those for the Figeh side spring (1500 m) and the Harouch spring (1300 m). The groundwater in the Barada spring seems to be recharged in a catchment area with a mean elevation of about 1250 m. The temporal evolution of stable isotope concentrations, tritium content and hydrochemistry show the existence of an interconnection between the aquifers of the Figeh main spring and the Figeh side spring, especially during flood periods. The distinct independent isotopic composition of Harouch spring from those of Figeh main and side springs suggests no interconnection with the Figeh aquifers. Adopting a model with exponential time distribution, the mean turnover time (residence time) of groundwater in Figeh main spring was evaluated to be 50 years. On the basis of this evaluation, a value of about 3.9 billion m 3 was obtained for the maximum groundwater reservoir size. © 1997 Elsevier Science B.V.