A storm water interceptor comprises an input conduit connected to a first treatment tank for delivering storm water to the first treatment tank and having an obvert elevation. Also, the interceptor comprises a lower conduit having an invert elevation, a substantially horizontal orifice at a first end connected to the first treatment tank and an exit orifice at an opposite end connected to a second treatment tank, whereby the substantially horizontal orifice at the first end of the lower conduit is below the invert elevation of the lower conduit. The interceptor further comprises an overflow conduit connecting the first treatment tank to the second treatment tank, whereby the overflow conduit is connected to the first treatment tank at a location above the obvert elevation of the input conduit. As well, there is an output conduit having a substantially horizontal orifice at a first end connected to the second treatment tank and an exit portion extending away from the second treatment tank, whereby an invert elevation of the output conduit is above an obvert elevation of the lower conduit, and whereby the substantially horizontal orifice at the first end of the output conduit is below the invert elevation of the output conduit. More than two treatment tanks may be connected in a cascading manner using the same general components and principles as an interceptor having two treatment tanks.