this discharge means may be an orifice or other hydraulic control a pump or any other conveyance that has the capacity to regulate the flow rate a pump for example may have a control or other means to limit and control the rate of flow through the pump the regulated discharge delivers the water to a second conduit 104 which delivers the water to the filter 203 the filter 203 is a device such as that described in my prior copending patent application ser no 10 040 611 filed jan 9 2002 and entitled filtering system for runoff water intended to remove both dissolved and particulate pollutants from water by use of a filter media the filter 203 may use any of various types of media to accomplish this removal and the media may be tailored for the specific contaminants expected in the stormwater runoff the water passes through the filter 203 and then enters a conduit 105 which delivers the treated water to an outfall such as a river the runoff water may vary from a very low rate to a very high rate at high rates the filter 203 is inefficient the reservoir 202 is preferably so big that it will hold all the water from a prolonged hard rain lasting several hours but the outlet pipe of the reservoir is so small or has a restriction limiting the flow or has other suitable means for controlling the flow so that the flow rate therethrough is not only within the capacity of the filter but takes at least one hour to drain the reservoir the function of the reservoir 202 and the pump 103 or other.