Graphing Controlled and Experimental data same graph?

Hey everyone, I'm new to this forum but I could really use some help. I'll try to keep my question as brief as possible and hope to get and answer!

Basically I have done a lab in my bio class where we measure the heart rate of daphnia insects in distilled water (8 separate times) and then in Ethanol (2%, 4%, 6% and 8%) and Caffeine (1%, 2%, and 3%). I have begun my graph and have the BPM on the Y axis, and the % of Drug Used on the X axis, with different symbols for each chemical. My question is, how do I graph the constant of our distilled water control on the graph? I can't see a plausible way seeing as the X axis only effects the experimental drugs. Sorry if this is pretty basic, but I could really use any help I could get. Thanks Much!