<![CDATA[Cold brew coffee has gained popularity due to its smoother flavour, lower acidity, and reduced bitterness compared with hot-brewed coffee. However, scientific evidence on the influence of brewing water composition on cold brew quality remains limited. Variations in water pH and mineral content may substantially affect extraction efficiency, chemical composition, and product consistency, highlighting the need for guidance on water selection. This study evaluated the effects of seven brewing water types (mineral, drinking, alkaline, reverse osmosis, tap, distilled, and deionized) on the physicochemical (colour, pH, total soluble solids, and caffeine), antioxidant (total phenolic content, total flavonoid content, DPPH radical scavenging activity, and ferric reducing antioxidant power), and sensory (aroma, acidity, bitterness, aftertaste, and overall acceptability) properties of cold brew coffee prepared from light- and dark-roasted beans under controlled conditions. Brewing water type significantly influenced physicochemical and antioxidant properties (p < 0.05). Light-roasted coffee brewed with mineral water exhibited higher pH (5.47), total phenolic content (16.60 mg GAE/g), and total flavonoid content (6.28 mg QE/g), indicating enhanced extraction of bioactive compounds. Alkaline water produced greater antioxidant activity for both roasting levels, with DPPH radical scavenging activity ranging from 5.82–8.29%, while tap water resulted in a higher caffeine content (161.18–201.41 mg/100 mL). Sensory attributes showed no significant differences among water types (p > 0.05); however, reverse osmosis water achieved higher overall acceptability scores. Multivariate analyses (PCA and PLSR) confirmed that water composition strongly influenced extraction behavior and antioxidant functionality, whereas sensory preference was not directly associated with phenolic concentration. These findings demonstrate the critical role of brewing water chemistry in determining cold brew coffee quality and provide quantitative guidance for water selection.]]>
