1 above, but substitute cola for the vinegar and water mix. Although cola is an effective cleaning product, it leaves a sticky residue that has to be removed even after the shower head is otherwise clean. The answer lies in our psychology and how we are wired to purchase things even if we don't need them. For this method, you can squeeze lemons or purchase a bottle of lemon juice. Lemons are similar to vinegar in that they are acidic by nature.