A large percentage of sicknesses and diseases in the world are caused by polluted water. This study examined the water purifying property of mushroom Lentinus squarrosulus Mont. Untreated water samples were obtained from a bottling water factory in Rivers State, Nigeria and subjected to physicochemical and microbiological analysis within 24 hours of collection to ascertain the contamination level. Sterilized sawdust was bagged, inoculated with mushroom spawn and allowed for 2 weeks to colonization the substrate. After the third week, the colonized substrates were ready for mycofiltration. Holes were bore in the middle of the substrate using sterilized stainless spoon and the untreated water sample was dispensed into the holes and allowed to filter through into a sterile container. Collected filtrates were taken to the laboratory for analysis. From the results obtained, the filtrate with L. squarrosulus, reduced the electrical conductivity (µs cm^-1) from 804.5 to 225.5, total dissolved solid (mg L^-1) from 378 to 114, total suspended solid (mg L^-1) from 7 to 2, nitrate (mg L^-1) from 0.1955 to 0.116, phosphate (mg L^-1) from 0.945 to 0.49, turbidity level from 10 to 4, biological oxygen demand (mg L^-1) from 6.72 to 5.12, dissolved oxygen (mg L^-1) from 7.36 to 5.12 and chemical oxygen demand (mg L^-1) from 6.29 to 6.08. L. squarrosulus exhibited a remarkable reduction in turbidity, total heterotrphic count and total coliform count, which made it a potential water purifying agent. The ability of L. squarrosulus to control and reduce water-borne bacterial diseases is beneficial to those who cannot afford or have access to clean drinking water in developing countries.