We designed, fabricated, and evaluated a monopole water antenna (WA) filled with pure water. A 2.4 GHz patch antenna (PA) was used for measurement comparison, and the current density distribution and 3D field strength radiation distribution and reflection coefficient of the PA had a fundamental mode and a higher-order mode at 3.5 GHz, whose polarization was 90 degrees different. The 2.4 GHz monopole WA could receive only the fundamental mode of the PA. The 3.5 GHz WA could receive the higher-order mode of the PA by rotating the WA by 90 degrees. The transmission coefficient of the 2.4 GHz WA decreased with the square of the spacing, similar to the spatial propagation characteristics of electromagnetic waves. Almost the same results could be expected if planar or three-dimensional antennas were used instead of monopole electrodes.