How did Shri Rama leave his bodily form? Did he take a Jal Samadhi? If yes, what is a Jal Samadhi?
How Lord Rama left his mortal body is described in this section of Uttar Kanda of Valmiki Ramyana:
Valmiki Ramayana Uttar Kanda Section CXXIII
HAVING thus gone for more than a half Yojana, the descendant of Raghu espied Saraju of holy waters flowing towards the west. And having crossed that river of rising waves to some extent, Rama, with his followers arrived at the place where he should give up his person. Thereupon at that moment, Brahma, the grandfather off all encircled by all high-souled deities and with hundred kotis of celestial cars, arrived there where Kakustha had addressed himself to repair to heaven. The aerial way was full of lustre but its brilliance was increased the more by the native effulgence of the inhabitants of heavens, always performing pious actions. There blew the holy. fragrant and delightful winds and there fell profusely celestial flowers from the hands of the deities. The place was filled with the noise of hundreds of bugles sounded by Gandharbas and Apsaras. And then Rama prepared him- self to descend to the waters of Saraju. Thereupon the Patriarch gave vent to the following accents from the welkin—"Come O Vishnu; may good betide thee; by our good fortune thou art coming here; 0 Raghava hear—0 thou having mighty arms, do than enter here with thy brothers, resembling the celestials in brilliance in whatever form thou liken—either in that of the sky or in thy own Vishnu form. Thou art the refuge of the creatures—nobody knoweth thee. Thou art above the range of thought ; great immortal and imperishable; nobody knoweth thee save Maya, having wide eyes, thy former spouse. Do thou enter here thyself in whatever effulgent form thou likest." Hearing the words of the Patriarch and determining everything the high-minded Ram entered there bodily with his brothers in his Vishnu form. Thereupon all the celestial: Sadhyas, Marutas, headed by Indra and Agni worshipped that deity, Vishnu. So did all the celestial Rishis, Gandharvas Apsaras, Suparnas, Nagas, Yakhas, demons, Danavas and Rakshasas. Thereupon eulogising him the celestials said :—“ Our region is now freed from sins and all here have been delighted and all their desires have been fulfilled." Therenpon the highly effulgent Vishnu said to the Patriarch Brahma:— “ lt behoveth thee, O thou of good vows, to allot to those people their proper regions. These illustrious ones have followed me out of love. They are worthy of my respect for they are my devotees and have renounced their persons for me." Hearing the words of Vishnu, the lord Brahma, father of all creatures, said :—-All these people who have come here shall go to the region named Santanaka. This region is intended even'l'or him, who though born in the most degraded state, thinks of all objects as Vishnu. There is no question about their attaining to this region who, out of devotion, have followed thee and renounced their persons. This region has all the attributes of the Brahma region and is next to it. The monkeys and bears shall enter into their respective celestial forms. They shall enter into the deities from whom they had respectively originated. Sugriva shall enter into the Sun’s region. And they shall obtain their respective lathers’ forms among the celestials present." The lord of the deities having said this, all those who were present at the holy pilgrimage of Gopratra" descended into the waters of Saraju with eyes lull of tears of joy. Having bathed there, given up their lives delightedly and renounced their human forms they ascended the celestial cars. And having obtained the waters of Saraju, hundreds of those that were born in the race of birds attained to the land of immortals obtaining the respective celestial forms (they had before). And in those celestial forms, they looked ei’fulgent like the deities. And going to the waters of Saraju all objects, mobile and immobile, having bathed there, repaired to the excellent celestial region. Having renounced their bodies in the water thereof all the bears, monkeys, and Rakshasas attained to the land of deities. Having thus settled in heaven all those arrived there the father. of creatures with the deities, delighted and happy, repaired to the highest heaven.
Hence from above it is clear that Lord Rama directly changed into Vishnu form after entering water of Sarayu. In one way it can be interpreted as Jala Samadhi too as Lord Rama human form is ended there due to entering in water. But it isn't exactly Jala Samadhi as Lord Rama directly changed into Vishnu form.
Giving up life by entering in water or giving up life by the aid of Jala Tatwa is known as Jala Samadhi..