This study evaluated the physicochemical properties of potable water (PW) treated with atmospheric cold plasma (ACP) with two different gas compositions (80% nitrogen + 20% oxygen and 90% nitrogen + 10% oxygen). PW samples, varying volumes (30 and 500 mL), were treated for 5 and 10 min. The stability of plasma-activated water (PAW) and its physicochemical properties, including pH, electric conductivity (EC), oxidation-reduction potential (ORP), nitrate (NO₃^–), nitrite (NO₂^–), and ozone (O₃) was assessed at room temperature (22 ± 2 °C) over a 30-day storage period. The results showed that increasing the plasma treatment time and reducing the water volume led to higher values for all measurements except pH. The results also showed that the volume of the water and discharge time notably influenced the physicochemical properties and activity of PAW. Specifically, pH, EC, and NO₃^– concentrations remained stable for 30 days without significant changes (p > 0.05). Conversely, the ORP decreased significantly with the storage time, as O₃ concentration diminished to zero within a few hours after PAW generation, and the NO₂^– levels decreased to undetectable levels by the third day.