An isolation device and method are provided for isolating a plumbing system of a premises from a potable water source if permissible input water pressure parameters are violated. After the plumbing system has achieved a desired input water pressure, the isolation device places the plumbing system in an isolated state and only removes the plumbing system from the isolated state if the isolation device detects a demand for water from the plumbing system and if the isolation device determines that permissible input water pressure parameters are not being violated. Once the demand no longer exists, the isolation device returns the plumbing system to the isolated state.