We found there are some habit from foreman or end consumer when they go to the parts shop to buy the waterpump assembly for their car.
Once the shop give them the waterpump they wanted, first, of course they will open up the box and check the condition on the waterpump, that is normal.
Secondly, they will start to turn the waterpump fan on the pulley side of the waterpump to check if the fan are moving smoothly, we can say that nearly 100% will do this kind of action, and most of us may think it is all right to do this.
For your info, there are mechanical seal install inside the waterpump where the area of the waterpump fan is turning. This type of mechanical seal is to prevent the leakage of water in that area, and don't be surprise that it work more effective when it had water inside.
By turning the waterpump fan without any water as medium in it, will scratch the mechanical seal of the waterpump, hence damage the surface of the mechanical seal which will cause it life span more shorter and leakage will occur sooner than it normal will be.