Studies have recently focused on microplastics (MPs) in tap and drinking water. Directly comparing the results of different studies is difficult owing to the use of various methodologies. In particular, a study of particles on a part of the filter to reduce the analysis time can lead to uncertainty regarding the number of MPs in tap water. In this study, the analysis of particles on the whole filtration area using a Fourier-transform infrared (FTIR) microscope was achieved in approximately 1 h using a filtration unit with a smaller filtration area (0.13 cm2) and a large-opening (26 μm) filter. Forty-two samples collected from five countries were analyzed using this method. The concentrations of the MPs at each site ranged from 1.9 to 225 particles L−1, with a mean concentration of all samples of 39 ± 44 particles L−1. The size ranged from 19.2 μm to 4.2 mm. Fragments were the predominant shape while fibers and spheres were also observed. Based on a combination of the shape, size, and chemical composition of the MPs, we discussed their sources. The MPs could have caused contamination after processing by a water treatment plant because we detected a significant number of polyester fibers > 100 μm, which were previously detected in the air, and PVC fragments > 50 μm, which are often used in water pipes. This study proposed technical improvements to the whole filtration area technique to detect MPs in tap water.