In ponds, controlling the water level is essential to prevent flooding of the surrounding area. This is done by overflow pipes. A pipe is placed in the bank. The end of the pipe is set to the desired water level. When the level of the water reaches the inlet, water starts to flow into the pipe. The water is diverted to a storm drain or runoff drain. The end effect is the water level in the pond never rises above the pipe. This is an extremely simple system of passive control, yet it works. Clemson University installed such a system to maintain the water level of beaver ponds.
Te level of water in the toilet tank is controlled by a float and valve system. As water fills the tank, it raises a float. When the float reaches a certain level, it trips a shut-off valve. While a flush toilet is very commonplace today, this was not always the case. In the 1800s people used outhouses and buckets for the disposal of human waste, which was very unsanitary. Realizing a sanitary method was necessary, designers worked to develop a flush toilet system. In 1861 Thomas Crapper patented the water tank part of the toilet. The tank part was called a "water closet." Today, the correct technical term for a toilet is water closet.
To electrically control water level in tanks, a float on-off switch is used. The float is mechanically connected to an on-off switch. When the float reaches a certain level, it turns the switch from off to on. The switch is wired to a pump, and it turns the pump on. Texas A&M University describes a project that uses such a system to control the water level in a waste water system. Ohio State University also describes a tank design that uses a float switch to control water levels.
The Folsom Dam in Sacramento, California must constantly control the water level of its reservoirs. This is a grand-scale system of level control, since hundreds of thousands of gallons of water are involved. Control is achieved by a system of gates. When the water level of the reservoir reaches a certain level, bypass gates are opened, allowing water to flow past the dam and into the American River and flood control lakes.