I just noticed that my pressure vacuum breaker, which provides backflow protection by keeping my lawn sprinkler water separate from my house-water, is leaking. I'm having a guy in on Tuesday to check it out. I'm concerned about health issues if the backflow device is compromised. How likely is it that the lawn water and house water could mix if in fact the PVB is broken? Would appreciate answers from plumbers familiar with the subject. Thanks in advance - Brian.