The 404 Inertial Pump is a cost effective option for groundwater monitoring. It's simple and reliable inertial pump design consists of a riser tube fitted to a one-way foot valve. The inertial pump or foot valve is easy to operate at shallow depths, and it can function as a surface-pumping mechanism. The 404 inertial pump is also a simple and effective alternative to using a bailer. As with a bailer, the most important part is the check ball, located in the foot of the pump. Because of the check ball's placement, the Wat inertial pump is commonly referred to as a foot valve. Available in several sizes, these foot valves and tubing are suitable for most well diameters and other sampling applications. A 1/4” (6 mm) Mini Inertial Pump is also available for use with CMT Multilevel Systems. To obtain samples, the user hand-threads the foot valve onto the tubing and then lowers it to the desired depth in either a well or borehole. It is then lowered and raised approximately 6” - 12” (15 - 30 cm). Water is forced into the tubing as it moves down and is retained as the tubing is raised, which allows the water to gradually rise until it is eventually expelled above ground. Manual use is simple, but surface-pumping mechanisms powered by electricity or gasoline are also available.