A sanitary check valve arranged between a drop and outlet pipes in a water well casing that will prevent operate to block a back flow of water through the drop pipe when pumping from a water source is discontinued as could contaminate that water source. The valve is for fitting into an actuator fitting body that mounts between the drop and outlet pipes opposite ends and includes a side plate for releasable coupling to a separate actuator mount that connects through the well casing and includes a drain pipe. The drop and outlet pipes fitted to the fitting body are lowered into the well casing to where the side plate edges slid between parallel sides of the mount, coupling the assembly together such that an upward water flow moves the float valve off of the drop pipe end to pass that flow through the outlet pipe for use, and, when that upward flow is stopped, the valve closes over the drop pipe end and opens to the mount drain pipe to a water flow that dumps outside the well casing.