Johannes Vermeer would have made a great interior designer. He knew how to create overall harmony in his paintings, all interiors, while allowing essential elements to "pop." And unlike most painters of any era, he used particular items in common household scenes to enliven his work. Most painters simply blur out any items that compete with the central subject matter. Vermeer included and harmonized many elements and enlivened his now priceless works in the process.
Young Woman with a Water Pitcher dates 1665-6. Oriental rugs were prized items of the well-to-do, so much so that they were rarely used as rugs. In this case the red rug with blue highlights serves as a table cover.
Veremeer may have cheated the blue in the rug to a brighter hue to balance the brilliant blue dress of the the girl opening the window. Or the blue elements in the rug could have been made of silk and "popped" the way he shows in the painting.
When the rug is on the floor, it tends to support the design of the room. In this painting as a table cover, it complements and counterbalances the overall blue atmosphere and the girl's dress.
Many thanks to the website Essential Vermeer, an outstanding resource for in depth study of this outstanding artist.