Therapit Trolling

I was in the middle of a therapy session with my therapist and my Atheism came up as a topic of discussion; as part of his argument for me to convert to Christianity, he stated that 1+1 doesn't always equal 2.
He based his assertion that 1 drop of water combined with another drop of water yields 1 drop of water.

So what would be a could counterargument?

>>1
You could mention how if the question was meant as a mathematical operation, then he should conform to the accepted rules of arithmetic, and if he deviating from them, then he should preface his query with the necessary information, or else he is being dishonest, which his god would strongly disapprove of, as it is a form of lieing and he is a dirty dirty dirty filthy fucking LIAR and should burn in hell for such a piece of pretzel logic bullshittery.