Isnaan, is a derivative of asnaan, and is a word which appears is the Sikh scripture, Guru Granth Sahib, meaning to bathe, cleanse, purify, or otherwise perform ablution.
Sikhism's code of conduct instructs the devotee to rise early and perform isnaan, bathing both body and soul. The body is to be cleansed in water, the soul cleansed in contemplation of the divine.
There is a saying which goes "Sarovar pani - Isnaan bani," which signifies that, "In the sarovar one bathes in water, but true cleansing is found in the scripture."
Most gurdwaras have some kind of bathing facility avaliable. Many historic gurdwaras are constructed close to a sarovar, or water source, such as a tank, well, fountain or pool which is available to all visitors and devotees for bathing. Certain of these sarovar are thought to have sacred or curative properties capable of healing both body and soul. There are legends of healing having taken place when a leprous, or cancerous, person performed isnaan by bathing in the water of sacred pool where scripture is continually recited. Some believe that performing isnaan by bathing in sacred waters, especially while reciting scripture, can absolve and enlighten the soul, liberating one from the cycle of transmigration and being born endlessly into existences.
Any Initiate preparing for the Amrit Baptism ceremony is to perform isnaan, bathe the body, wash the hair and cleanse the thoughts, mind, heart, and soul by reciting Waheguru, meaning Wondrous Enlightener.
Shabad by Guru Raam Daas: "Oudham karae bhalkae parbhaatee isnaan karae anmrit sar naavai||
Upon arising early in the morning, one is to bathe, and cleanse oneself in the sacred pool of immortal nectar." SGGS||305