Estimating groundwater infiltration into sewer systems is important for wastewater treatment operators and municipalities. This paper presents an approximate solution for steady-state groundwater infiltration into sewer systems through line defects. The groundwater table was assumed to be horizontal and the aquifer homogeneous and isotropic. Mobius transformation technique and equivalent circumference method were introduced to solve the governing equation. The infiltration rate is found to be controlled by the hydraulic conductivity of the surrounding soil, the total hydraulic head above the sewer pipe, the size of the sewer pipe, the position of the defect, and the size of the defect.