Abstract: A device for collecting liquid samples of runoff water. The device is configured such that it does not collect any sample until a predetermined amount of runoff water has flowed. At that time, a predetermined water quantity is allowed to enter a water storage area. Once this water storage area is full, a closure occurs, and further water cannot be trapped. In the most preferred embodiment of this invention, the entire structure is formed of PVC plumbing materials. A first embodiment of the invention is adapted to be mounted vertically and uses a check valve and a float. A second embodiment of the invention is adapted for use in a runoff sewer, and collects water when the water flow is above a certain height. When the water flow becomes above a second height, a closure mechanism is activated, preventing further water from being trapped.