You might have noticed that the Pump System can move when you try to attach the Pump Addition. Check the Hydro Dynamics Robot Game Field SetUp Guide. It says, "Secure the model to the North border wall within the marks." There are no Velcro marks on the field mat. So, it probably means use Velcro on the wall. See picture from another FIRST guide:
If you are having a little trouble with the Water Treatment model working properly (and you know you built it correctly with gear meshing not too tight or loose), double check the gear to the conveyor belt - the bar across the belt should be as pictured when you attach the gear.
Then it should work perfectly...