A porous water-treating material comprising cut porous strands each comprising a resinous matrix material which consists essentially of a thermoplastic polymer material or a mixture thereof with an inorganic particulate material. Each strand having a number of pores connected to each other and an irregularly rugged peripheral surface which has a ratio in diameter of a circumscribed circle to an inscribed circle in any cross-sectional profile from 1.10:1 to 5.00:1 and a ratio of the distance between circumscribed lines to that between inscribed lines in any side projection profile of from 1.10:1 to 3.00:1. The cut porous strands are prepared by melt-extruding a resinous mixture of the resinous matrix material with a blowing agent at a temperature higher than the melting point of the thermoplastic polymer material and the thermally decomposing point of the blowing material so as to cause the strands to have a number of pores and an irregularly rugged peripheral surface thereof.
