A method for membrane filtration purification of suspended water, comprising filtering the suspended water under an external pressure through a porous hollow fiber membrane comprising a polyolefin, a copolymer of olefin and halogenated olefin, halogenated polyolefin or a mixture thereof and having an open area ratio in an outer surface of not less than 20% and a pore diameter in a minimum pore diameter layer of not smaller than 0.03 .mu.m and not larger than 1 .mu.m.