1, life considerations. If ancient people didn't drill a well or put a big water tank at home, it would be extremely inconvenient to use water. People who are close to the water source are fine, while those who live far away from the water source have to go several miles or even farther to fetch water. Adults always like to tell the story of "three monks have no water to drink" to warn children not to shirk their work and learn to cooperate. However, it also shows that water was scarce in ancient times, and even they needed to transport water from far away places.
2. Security considerations. The main components of ancient buildings are wooden materials. In case of fire, the water tank at the door of the house can put out the fire in time.
3. feng shui considerations. It is good to settle down in a place surrounded by mountains, especially rivers or springs. If it is unrealistic, you have to open a well or put a water tank at home.