I think these water tanks not only have fire prevention function, but also have a certain feng shui status. After all, it is in the palace, and the people in the palace are basically superstitious. After all, they have been sitting in such a high position, and it is very normal to cherish their lives. They are also very concerned about Feng Shui. Therefore, the placement of these tanks should not only be able to put out the fire as quickly as possible, but also conform to a certain feng shui status, because if these tanks make the feng shui of the palace worse, it is very unlucky.
In fact, these water tanks also have a very auspicious name, called auspicious tanks. In ancient times, people were very afraid of fire. Even in their eyes, living was something closer to the gods, so when they caught fire, they would not say that they were on fire, but that they had walked away.
In fact, these tanks are filled with water all year round. In winter, in order to prevent the water from freezing, they leave a small gap between the bottom of the tank and the ground when they put it down, so that they can make a fire under it to prevent the water from freezing in winter. They will also put on a cotton "suit" for the tank.
The above is my opinion, I hope it will help you.