It is not necessary to rinse with water after using Listerine mouthwash. In fact, to get the best out of the product, you should use Listerine mouthwash without rinsing with water afterward.
The reason is because Listerine contains powerful antibacterial and deodorant ingredients that kill bacteria and eliminate bad breath. When using Listerine mouthwash, you should pour a sufficient amount into your mouth and gargle for about 30 seconds for the best effect of the product. You can then spit out the waste water without having to rinse it with water.
However, if you find the smell and taste of Listerine mouthwash too strong or unpleasant, you can rinse with a small amount of water to reduce that discomfort. However, if you can tolerate the smell and taste of the product, not needing to rinse with water will help the effects of Listerine last longer and achieve the best effect.