A medium for water culture has a porous substance and photocatalyst particles formed of titanium-based compound particles that are supported on the porous substance, have absorption at a wavelength of 500 nm in a visible absorption spectrum, and have an absorption peak at 2,700 cm−；1 to 3,000 cm−；1 in an infrared absorption spectrum, in which a metal compound having a metal atom and a hydrocarbon group is bonded to the surface of each of the titanium-based compound particles through an oxygen atom.
