The scarcity of water resources in Jordan imposes strategic difficulties for economic development and has been a basis for disputes with neighbouring countries. A welcomed discovery in the past decade is the occurrence of artesian thermal groundwaters at Mukhebeh in the lower Yarmouk valley, which produce over 40 × 106 m3 year⁻¹ of fresh water. The principal resources occur in the upper B2 Formation (Campanian), a limestone overlain by confining marls of the B3 Formation (Maastrichtian). Additional resources are found near by along the eastern Jordan Rift Valley (JRV), in the underlying A7 limestone (Turonian).

Groundwaters in the Mukhebeh (B2) wells are low salinity (500 mg l⁻¹ TDS) Ca(Mg)-HCO₃ waters with elevated HS⁻ attributed to sulphate reduction driven by oxidation of aquifer-derived organic matter. The JRV (A7) groundwaters are similar to the B2 waters with the exception of higher Mg²⁺ and HCO₃⁻ attributed to dolomite dissolution and sulphate reduction. Groundwaters from JRV 1 and the Maqla spring at Mukhebeh are NaCl waters with a strong Ca(Mg)-HCO₃ facies (900 to 1000 mg 1⁻¹ TDS). The elevated temperatures of all groundwaters (30 to 54°C) can be attributed to heating along a local geothermal gradient of 2.5°C per 100 m. Departures from this gradient are due to vertical flow in fault zones and possibly to the local influence of an intrusion (MK-7).

All groundwaters are characterized by a late Holocene (modern) stable isotope signature. Groundwaters from the high yielding upper B2 aquifer (MK wells) have a δ¹⁸O/δ²H composition demonstrating recharge in the B2 outcrop region, near and to the east of Irbid, within the Yarmouk River basin. Conversely, the deeper A7 aquifer groundwaters (JRV wells) are recharged at a lower elevation in the rift valley margin, where incised wadis have exposed these strata. The deepest Al to A6 strata (Magla spring and JRV 1 well) contain the isotopically most depleted groundwaters. Based on comparison with precipitation and phreatic groundwaters, recharge in the highest landscape of northern Jordan is likely, although a source of recharge from the northern Golan region of Syria cannot be excluded.

All thermal waters are essentially ³H-free. Estimates of their mean subsurface residence times have been constrained on the basis of ¹⁴C inDIC Significant corrections have been made for ¹⁴C-dilution processes including carbonate dissolution, sulphate reduction and a tertiary process involving either incorporation of mantle CO₂ or matrix exchange. All dilution processes were quantified on the basis of geochemical and ¹³C mass balance equations. Modelled ages show that recharge for most B2 and A7 groundwaters occurred during the late Holocene (recent to 5 ka BP).