A systematic study of individual precipitation (wet-only) events (n=91), collected for three years (2000–2002) during the period of SW-monsoon (June–September) from a semi-arid region (Ahmedabad, 23°03′N, 72°38′E) in India, reveals that rainwater is characteristically alkaline in nature (pH range: 5.2–8.2, Av.=6.7). The ionic ratio of Cl⁻ and Na⁺ in each event closely follows that of sea-salt composition. The measured abundances of Ca²⁺ (5.5–1057μeql⁻¹), Mg²⁺ (1.5–251μeql⁻¹) and HCO₃⁻ (8–836μeql⁻¹); non-sea-salt (nss) components of Ca²⁺ and Mg²⁺ varying as 94–99% and 0–84%; and linear regression parameters among (nss-Ca²⁺+nss-Mg²⁺) and HCO₃⁻ (slope=0.71, r²=0.96) all tend to suggest that crustal sources dominate the chemical composition of precipitation. The concentrations of acidic constituents SO²⁻₄ and NO₃⁻ vary over a wide range, from 4.8 to 431 and 1.0 to 115μeql⁻¹, respectively; and that of NH₄⁺ varied from 1.7 to 220μeql⁻¹ and K⁺ as 0.6–53μeql⁻¹. A significant impact of anthropogenic sources on rainwater composition is evident based on the nss-fraction of SO²⁻₄ (67–99%, VWM=86%) and equivalent ratio of nss-SO₄²⁻/NO₃⁻ (0.8–6.7, VWM=2.5). With the exception of NH₄⁺, concentration of an individual species in a rain event is largely controlled by the precipitation amount. The inter-annual variations in the volume-weighted-mean composition are not significantly pronounced; making this a representative data set for the study region.