To prevent permeation of an impurity by fitting a guide pipe on which a strainer is arranged by drilling a ground and injecting water underground through a filter for oil adsorption and sediments in a cartridge filter by introducing it to the inside of the guide pipe from a ground surface.

A guide pipe 11 on which a strainer 11a consisting of a striation in the vertical direction or a circular through hole, etc., is arranged is fitted into a hole 10 drilled on a ground. Thereafter, a cartridge filter 20 consisting of a cylindrical casing 21 having a large number of water passing holes 21b on its side surface and a blank cap 21c on its lower surface, a filter 23 for sediments installed in the inside of the casing 21 and an oil adsorption filter 22 is installed in this guide pipe 11. Thereafter, water (a) introduced to the inside of the guide pipe 11 from a ground surface 2 flows in underground through a strainer 11a by passing the oil adsorption filter 22 and the filter 23 for sediments. Consequently, it is possible to prevent ground subsidence by returning the water from which oil and sediments are removed to the underground.