This research is an attempt to monitor the level of heavy metals (As, Pb, Cd, Zn and Cu) and major cations (Na, K, Ca, Mg) and anions (HCO₃, CO₃, SO₄, Cl) and stable isotopes ²H, ¹⁸O ,δ¹³C) in ground water and surface water (Soan River), Rawalpindi region, Pakistan before and after monsoon period. Total of 88 water samples from River Soan (44) and groundwater samples (44) in vicinity of River Soan were collected before and after monsoon. All the cations were analyzed using Atomic Absorption Spectrometer whereas Isotope analysis were carried out using ICP-OES at PINSTECH, Islamabad. Results indicated that the EC in all water was lowered after monsoon whereas pH in all the water samples (ground and surface) ranged from 6.80 to 7.86. No changes were observed in Sodium concentrations. Potassium in surface water shows significant decrease after moon soon (14.28 to 3.05 ppm) whereas in ground water it does not change significantly. The mean concentration of calcium in surface water samples was increased from 23.46ppm to 40 ppm after monsoon period and similarly Magnesium concentration decreased both in surface and ground water after monsoon period. Ca-Mg-type of water predominated in both seasons (pre-monsoon -83%) and post monsoon (90%) suggests no significant change in the hydro chemical facies. The results of trace metals showed increasing trend due to heavy precipitation. The mean concentration of Zn increased from 18.3 ppb to 67 ppm in surface water, and from 9.48 ppb to 27.39 ppm. Similarly, increasing trend was observed in the mean concentration of Cadmium in surface water (0.21 ppb to 16.9 ppb) whereas in ground water the concentration was low. The mean Pb concertation was also increased in surface water (from 4.03 ppb to 48.44 ppb) and in ground water (from 7.42 to 14.59 ppb) after monsoon. Mean copper concentration also increased from 1.90 ppb to 5.73 ppb in ground water. 95 % of the water samples were found to be contaminated with fecal coliform suggesting sewage mixing. Post monsoon samples show depletion in δ¹⁸O as compared to pre monsoon samples.¹³C value is depleted suggesting sewages pollution of the Soan River and its surrounding area. It is concluded from results that the rainwater washed metals accumulated on the surface and/or vadose zone and percolated the high concentrations to the groundwater