"Tianshui" is a name, because of what it got, how it came to be. Let me elaborate below for you:
Tianshui was a vassal of the State of Qin during the Zhou Dynasty, and was called Yi County during the Spring and Autumn Warring States Period, and was named Shangyi in the Qin Dynasty. So why was it called Tianshui later, and there is a magical legend behind it.
Legend has it that in the third year of emperor Yuanding of the Eastern Han Dynasty, Shangyi experienced an unprecedented drought. That summer, the sun was like fire, the climate was hot, but it had not rained for a long time. Watching the crops in the fields dry up day by day, drinking the little muddy and bitter water left in the river, the people were anxious and prayed to the gods for rain every day. It may be that people's sincerity finally touched the heavens, and in the middle of the night, just when people were falling asleep, there was a sudden deafening thunder in the sky. The thunder mixed with lightning seemed to roll from the sky, getting stronger and stronger. For a time, the earth was fiercely winding, flying sand and stones. People were frightened by this formation and thought God was angry. At this moment, a red light appeared on the ground, and then the earth continued to shake, as if it were about to crack. Suddenly, with a thunderclap in the sky, a deafening noise came from under the ground, and the earth really cracked, as if it had opened its mouth, and a white mist drifted from the crack. At the same time, he saw a thick river water falling from the sky, just into the cracked ground, as if The Heavenly Father knew that the earth had been thirsty for a long time, and used the water of the Heavenly River to quench his thirst. The scene was spectacular, and people's eyes widened in amazement. The water of the Heavenly River flowed for a long time, until the wind stopped, the thunder stopped, and the earth returned to tranquility. Curious, people ran to the crack in the earth to see that there was a large lake, and the water in the lake was clear, transparent, sweet and delicious. For the next few days, the sky kept falling with drizzle, saving the whole world from drought and heat. With the moisture of the water, everywhere became green, the mountains were green, and the streams were babbling.
After such a change, people believed that it was the power of the gods, so the "Tianhe Flood" was passed on to the gods. In fact, according to our view today, this is likely to be just a natural phenomenon, a major earthquake. But people at that time could not explain this, so they called the lake "Tianshui Well", and also said that this water "does not dry up in spring, does not overflow in summer, and the four seasons are clear." Irrigated with this water, the seedlings grow stronger, the trees are verdant, and even the girls who raise them are particularly handsome. Since then, Shangyi has become a veritable oasis in Longshang, and the story of "water injection into the Tianhe River" has been passed down from generation to generation. At that time, in order to better manage it, the Han Dynasty decided to divide Longxi County (present-day Water District) into two counties. After hearing the legend of "water injection in the Tianhe River", Emperor Wu of the Han Dynasty aimed to build a city by the lake and set up a new county here, named "Tianshui County". Tianshui got its name from this.