Abstract: The disclosed apparatus relates to a public water system protection apparatus comprising: a single unit. The single unit comprises: a stop valve; and a check valve in fluid communication with the stop valve. The apparatus is configurable to couple to a customer water line and to prevent back flow into a water main. A public water system protection system comprising: a water main in fluid communication with a public water system; a customer water line in fluid communication with the water main and in fluid communication with a customer location; a public water system protection apparatus coupled to the customer water line and in fluid communication with the water main and in fluid communication with the customer location, and where the public water system protection apparatus comprises: a single unit. The single unit comprises: a stop valve; a check valve in fluid communication with the stop valve; and wherein the public water system protection apparatus is configured to prevent back flow into a water main.