Relatively simple instrumentation has been developed to measure and record rainfall and runoff on small urban areas draining to storm water inlets. The instruments include a tipping bucket rain gage, weirs and head sensing devices installed inside storm water inlets, and a multiple pen recorder. Runoff into as many as six storm water inlets is recorded at a single location. Controls are provided to operate the instruments automatically during storms. The occurrence of rainfall and runoff closes switches, sending pulses to the recording pens, and a synchronous record of the events is compiled on a single continuous chart. A chart speed of 1-1/2 in. per min permits evaluation of the data in small increments of time. Power is obtained from a 12-VDC storage battery. The equipment is designed to be installed with little modification of existing drainage facilities. Field tests and model studies were used to determine discharge characteristics of the inlet weirs.