NOVELTY - A sporulating microorganism which has protein and lipid degradation activity, is adsorbed on a filter medium (1). The microorganism (bacteria) is adsorbed at a density S of more than 105 CFU (colony forming units)/g of filter medium. The filter medium is then dried to a water content of 0.3-3%.    USE - For bath water purification and recirculation.    ADVANTAGE - The filter medium for bath water purification has good purification ability and has protein and lipid degradation action. A specified, heat-resistant microorganism is cultivated in a short time. The dried filter medium is easy to handle and enables efficient water purification.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) manufacture of filter medium, where:    (a) spores of a microorganism having protein and lipid degradation activity are added to water and a spore suspension is prepared; and    (b) the filter medium is immersed to the spore suspension and made to adsorb the spores;    (c) medium is dried at 40-50degreesC, reducing water content to 0.3-3%;    (2) a bath water circulation purifier comprising:    (a) a purifier unit (2) and circulating path for receiving bath water and returning purified water;    (b) heater (11) enabling harmful microbe elimination, by heating the bath water to 70-90degreesC;    (c) closed circuit which by-passes the bath comprising the purifier and heater; and    (3) culture method of filter medium microorganism in purifier unit comprises:    (a) heated bath water circulated in the by-pass closed circuit at 70-90degreesC, to eliminate common bacteria; and    (b) temperature of water is then reduced to 30-50degreesC and the water circulated in the by-pass path for 8 hours or more, at 30-50degreesC for culture of the microorganism.    DESCRIPTION OF DRAWING(S) - The figure shows the system assembly of purifier for bath tub water. The diagram contains Japanese writing.    Filter medium (1)    Purifier unit (2)    Ejector (3)    Ozonizer (4)    Photocatalyst (5)    Ultraviolet lamp (6)    Circulating pump (8)    Heater (11)    Bath tub (13)    Thermal sensor (14)