Abstract: Chemical injector comprises injector structure for injecting a solution from a reservoir into a flowing stream, usually water. The reservoir is at atmospheric pressure, and a chemical solution is withdrawn therefrom by Venturi action, with flow rate being controlled by passage size. Alternatively, an injector pump can positively pump the reservoir solution into the flow stream when the flow rate is too low for Venturi action. A flow control valve is also connected to a bottom portion of the piston of the pump to control the amount of chemical solution flowing from the reservoir to the flowing stream.