Japanese gardens always have water, either a pond or stream, or, in the dry rock garden, represented by white sand. In Buddhist symbolism, water and stone are the ying-yang, two opposites which complement and complete each other. A traditional garden will usually have an irregular-shaped pond, or, in larger gardens, two or more ponds connected by a channel or stream, and a cascade, a miniature version of Japan's famous mountain waterfalls.
In traditional gardens, The ponds and streams are carefully placed according to Buddhist geomancy, the art and science of putting things in the place most likely to attract good fortune. The rules for the placement of water were laid out in the first manual of Japanese gardens, the Sakuteiki, or "The Creation of Gardens", in the 11th century. (see "Literature" below.) According to the Sakuteiki, The water should enter the garden from the east or southeast, and flow toward the west because the east is the home of the Green Dragon (seiryu) an ancient Chinese divinity adapted in Japan, and the west is the home of the White Tiger, the divinity of the east. Water flowing from east to west will carry away evil, and the owner of the garden will be healthy and have a long life. According to the Sakutei-ki, Another favorable arrangement is for the water to flow from north, which represents water in Buddhist cosmology, to the south, which represents fire, which are also opposites, or ying-yang, and therefore will bring good luck.
The Sakuteiki recommends several different possible miniature landscapes using lakes and streams; the "ocean style", which features rocks which appear to have been eroded by waves, a sandy beach, and pine trees; the "broad river style", recreating the course of a large river, winding like a serpent; the "marsh pond" style, a large still pond with aquatic plants; "The mountain torrent style", with many rocks and cascades; and the "rose letters" style, an austere landscape with small, low plants, gentle relief and many scattered flat rocks.
Traditional Japanese gardens have small islands in the lakes. In sacred temple gardens, there is usually an island which represents Mount Penglai or Mount Horai, the traditional home of the Eight Immortals.
The Sakuteiki describes different kinds of artificial islands which can be created in lakes, including the "mountainous island", made up of jagged vertical rocks mixed with pine trees, surrounded by a sandy beach; the "rocky island", composed of "tormented" rocks appearing to have been battered by sea waves, along with small, ancient pine trees with unusual shapes; the "cloud island", made of white sand in the rounded white forms of a cumulus cloud; and the "misty island", a low island of sand, without rocks or trees.
A cascade or waterfall is also an important element in Japanese gardens, a miniature version of the waterfalls of Japanese mountain streams. The Sakuteiki described seven different kinds of cascades. It also notes that if possible a cascade should face toward the moon, and should be designed to capture the reflection of the moon in the water.