How does mixing lemon juice in hooka water affect the composition of the mixture?
The acidic water is probably protonating nicotine, causing it to carry a positive charge. Once charged, the resulting nicotinium cation will not be volatile, but rather, highly soluble. Based on this, I would expect that acidifying the water causes a much lower amount of nicotine  to be pulled through the exit hose (because it is trapped in the acidic water).