While saline solution is not strictly required for use with sponge electrodes, it is recommended. Plain water will work in helping the sponge to pass current, just not as well as saline solution. Water in and of itself is a very poor conductor of current. So in using just water, you’re essentially asking the sponge alone to work to pass current to the targeted area. By adding salt to plain water (saline solution), the electricity is able to actually jump from molecule to molecule through the solution, providing a better connection. In using a sponge well soaked with saline solution, the current encounters the least amount of resistance, providing the most effective, and most comfortable tDCS experience.