What we call "okayu" is rice cooked with more water than normal rice. What we call "zosui" is cooked rice boiled with dashi stock soup.

Okayu began to appear in documentary records around the 11th century. In Japanese homes, it is often made for babies or sick people.

"Shirogayu" is the basic okayu, without any flavor. Its hardness varies from a little softer than normal rice to a paste with almost no rice grains, depending on the percentage of rice and water. "Shirogayu" is often eaten with strong-flavored side dishes. One of them is "umeboshi", dried-plum pickles made by soaking plums in salt and drying.

Salted kelp and tsukemono are often eaten with Shirogayu. Tsukemono (pickles) are vegetables marinated in salt and rice bran.

In Japan, from ancient times, there has been a custom of eating Nanakusagayu on January 7, hoping for good health for the year. Nanakusagayu is porridge made by boiling rice with seven kinds of herbs; "seri (water dropwort)", "nazuna (shepherd's purse)", "gogyo (cudweed)", "hakobera (chickweed)", "hotokenoza (nipplewort)", "suzuna (turnip)" and "suzushiro (radish)". It is also said that ancient Japanese people expected that Nanakusagayu would give rest to the stomach that had weakened by excessive drinking and eating during the New Year holiday.

Japan has also a custom of eating "Komamegayu" on January 15. "Komamegayu" is made by boiling rice and red beans until they become soft. It has been said since ancient times that red beans have the power to ward off evil spirits. By eating Komamegayu, people hoped to ward off evil spirits and epidemic diseases. January 15 is a full moon day in the lunar calendar, so Komamegayu is also called "Nozomigayu" in the sense of okayu eaten with hope on the day.

"Chagayu" is eaten mainly in Nara Prefecture. It is made by boiling rice in water-based "hojicha"; roasted Japanese tea (green tea). It was originally eaten by monks of temples of the region from over 1000 years ago. In summer it is eaten chilled. Sometimes vegetables, potatoes and beans are put in.

Many Japanese make "zosui" when they have finished eating the ingredients of a pot dish. They put rice in the remaining soup of the pot dish and boil it. You can often order "Zosui set (a set of rice, egg, chopped green onion, etc.)" as an add-on at restaurants where pot dishes are served.