A water brush, also known as a water pen, is an art supply used in conjunction with watercolor pencils and solid watercolors. The barrel of the brush functions as a water tank, eliminating the need to carry a water container (bucket), making it extremely convenient for outdoor sketching and on-the-go drawing. Key Features: Built-in Water Tank: By gently squeezing the barrel, water is supplied to the brush tip, allowing for water flow adjustment. No Brush Washing Required: When you want to change colors while drawing, you can easily clean the brush by wiping the tip on a cloth or tissue while dispensing water. Portability: Many are compact with caps, making them easy to carry in a pen case.