But you still have the issue that the testing company is paid by the Navy.  How do you know the sample taken is the sample tested?

It's the same reason athletes will often take a second sample of blood to confirm the test.

And it doesn't even have to be monkey business - a mistake could have occurred on the first test 

This isn't a test to figure out why your tulips aren't growing.   Water is life - I personally would do a second test.  But again - that is me and I don't live in Admirals Cove