The objective of this study was to determine the effects of electrochemically activated drinking water (ECW) on milk yield, milk composition and somatic cell counts (SCC) in dairy cows. In Farm 1, as a controlled study, two groups of lactating cows were offered regular drinking water (n = 27) and ECW (n = 27) water dosed with 4 ppm of 29 mg/L of chlorate (Neuthox^®). The 54 cows were grouped into two groups, balanced by stage of lactation (111 ± 67 DIM) and parity (2.2 ± 0.4). Cows received water with or without ECW for 6 months. In Farm 2, a longitudinal study was undertaken with 140 lactating cows that were offered ECW for 5 months. Monthly records from milk yield and milk components were analysed from both farms. In Farm 1, SCC were lowered by ECW (162 ± 42 × 10³/mL) compared to no ECW animals (411 ± 202 × 10³/mL). In Farm 2, milk yield (from 35.5 to 32.7 kg of energy corrected milk) and milk protein (from 3.52 to 3.33 g/100 g) contents decreased across the months while SCC tended to decrease. Results showed that ECW could be useful for reducing SCC without detrimental effects on milk production and milk composition.