Find your backflow assembly. Above ground assemblies will be in a large, green/tan, rectangular box, more than likely located near your home or water meter. Below ground assemblies will have a large, green, rectangular lid. Once found, turn either handle on assembly to the right to turn water off. green, rectangular lid. Once found, turn either handle on assembly to the right to turn water off. Contact your local water department if you are unable to turn off water.