Storm water runoff first flush sampler

A storm water runoff first flush sampler is provided which includes at least one container which has a top and a bottom. A water collection device is also provided which has an inlet end for collecting water and an outlet end for discharging the collected water. The inlet end of the water collection device is located above the top of the container, and the outlet end of the water collection device opens into the container for filling the container with water. A device is also provided for venting air from the container as it is filled with water and discharging the vented air at a level above the top of the water collection device. This arrangement enables automatic termination of gravity flow to the container when water reaches the level of the water collection device. Also, the water collection device is provided with an aperture that releases the kinetic pressure resulting from water falling onto the inlet end of the water collection device, thereby preventing alteration of the composition of the original sample by additionally collected water. Further, the liquid collection device has a P trap which will prevent sediment from additional runoff water from entering the container after the container is full.