The use of magnetized water in concrete has significant effects on the properties of both fresh and hardened concrete. This study investigates the effects of both water flow rate into an electromagnetic field (Q) and magnetic field intensity (MFI) on the properties of self-compacting concrete (SCC). To this end, four base SCC mixes with water-to-cement ratios (W/C) of 0.35, 0.4, 0.45, and 0.5 were prepared using either tap or magnetized water. In the mixes with magnetized water, water was passed with different Q (9, 18, and 27 L/min) through electromagnetic field with different MFI (0.6, 0.9, 1.2, and 1.5 T) to be magnetized. The dosage of superplasticizer for each of the 52 mixes was adjusted to obtain a spread diameter of 650 ± 10 mm. Results showed that using magnetized instead of tap water increased concrete workability and improved the mechanical properties of SCC. The most positive effects of magnetized water were observed for MFI = 1.2 T and Q = 9 L/min so that superplasticizer consumption reduced by up to 34.1%. Moreover, compressive, bending, and tensile strengths of the concrete thus prepared increased by up to 34.1%, 52.4%, and 74.2%, respectively, despite the identical W/C ratios of the mixes.