In order to paint with watercolors, you need to gather pigments in tubes or as a pan set and a palette. You also need watercolor paper or another suitably absorbent surface, sable or synthetic watercolor brushes in a variety of sizes, and water in a jar or other container.
In addition to basic painting supplies, you may need to purchase an easel, depending on your working style and the location of the object or scene you are painting. Any paper with a weight of 140 or higher is preferable to avoid water warping. If you choose to purchase loose paper, you need an appropriately sized board to create a flat, durable painting surface. In this case, you should purchase large clips to hold the paper firmly in place on the board. Some basic brushes to consider purchasing include a #8 round red sable watercolor brush, a smaller #4 round brush for more detailed work and a one-inch flat brush for color washes. Typically, two containers of water are a necessary accessory. Use one container to dilute and wet the pigment, and use the other between brush strokes to clean the brush and avoid unintentional pigment mixing. You can use regular paper towels to dry and re-shape brushes after cleaning them.