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?

>>5
Don't be mad just because this guy proved your atheism to be irrational.