Abstract: Apparatus, systems, and methods are provided for regulating a fluid level provided in an animal watering trough. The components that are part of the apparatus, system, and method may include a housing having at least one side wall, base, and removable cover where the housing define a cavity that is configured to contain fluid. Also, the components include a fill valve positioned within the cavity of the housing for controlling a level of the fluid within the housing, an intake port that may be connected to a fluid supply, and an output port in fluid communication with the animal watering trough. The system may be configured such that when the fill valve is in a first position, the fluid is prevented from flowing between the intake port and the housing, and when the fill valve moves into a second position, the fluid flows via the intake port into the housing.