It is normal for the water tank to have water in it when opening the Xiaomi Robot Vacuum S40 for the first time.
For your reference, the reasons are as follows:
1. The Xiaomi Robot Vacuum S40 undergoes random inspections before leaving the factory, including a water tank inspection in which clean water is added to the tank for verification;
2. After the tank inspection is completed, the water is drained. It is normal to find residual water stains in the tank;
3. This is not a sign of previous use or a defect, but rather a standard part of the manufacturing and quality control process. The remaining moisture is harmless and does not affect the robot vacuum's performance.