The Mishna continues with its discussion of heating up food on Shabbat by turning to the question of heating water.
The Mishna relates a story about the people of the city of Tiberias, and they ran a cold-water pipe [silon] through a canal of hot water from the Tiberias hot springs. They thought that by doing so, they could heat the cold potable water on Shabbat.
The Rabbis said to them: If the water passed through on Shabbat, its legal status is like that of hot water that was heated on Shabbat, and the water is prohibited both for bathing and for drinking. And if the water passed through on a Festival, then it is prohibited for bathing but permitted for drinking. On Festivals, one is even permitted to boil water on actual fire for the purposes of eating and drinking.
Tiberias is a town on the shore of the Sea of Galilee founded by Herod Antipas (c. 18 C.E.). It was apparently founded on the site of earlier settlements, and according to some opinions in the Talmud (Megilla 6a) this was the site of the biblical city of Rakkat. At the outset, Tiberias was a town of mixed Jewish and gentile population. The Jewish population was not distinguished for its Torah scholarship. However, after the destruction of the Temple, important Torah scholars, such as Ben Azzai and Rabbi Meir, lived there. Its period of greatness came when the Sanhedrin moved there (c. 235 C.E.) and it became the seat of “the Great Council”, presided over by Rabbi Yehuda Nesia I. After him Rabbi Yohanan became its leading spiritual figure, and headed the yeshiva there. From that time, Tiberias was the Torah center of Eretz Yisrael. Most of the disciples of Rabbi Yohanan, particularly those who immigrated from Babylonia, lived and continued their studies there.
For many years, the people of Tiberias drew their water from springs adjacent to their city and not from the Sea of Galilee. However, the water from the Tiberias hot springs is not potable. Therefore, the people of Tiberias tried to use the hot springs to heat potable water, transported by means of aqueducts, by running a pipe through the hot springs.