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The circulation of groundwater is influenced by several factors, including permeability changes due to the dynamics of the stress field acting along tectonic discontinuities. Open faults can act as preferential pathways for the escape of crustal and subcrustal gases, such as CO₂, towards the surface, allowing their chemical interaction with meteoric fluids. Here, we present the first map of dissolved CO₂ partial pressure in the groundwater of Sicily, Italy. Based on the chemical analysis of 557 samples of groundwater, which were collected in wells and springs, we calculated the related CO₂ partial pressure (<i>P</i>CO₂) using PHREEQC software. The spatial distribution of the calculated <i>P</i>CO₂ values highlights a general homogeneity at the regional scale, interrupted by positive anomalies linked to the main seismogenic or volcanic areas. Faults work as preferential escape pathways for deep CO₂. The subsequent CO₂–water–rock interaction determines the chemical composition of circulating water. As a consequence, groundwater composition can be successfully used to identify anomalous degassing areas.