Due to the fact that the water from the reservoir goes by gravity of its pressure is very weak, which is one of the disadvantages of such a system.
The second disadvantage of this design is the need for constant tracking the operation of automation. Otherwise, the water will without a break to go beyond the tank and your house may be flooded. In order to avoid such an unfortunate situation, it is best to attach an overflow pipe to the tank, which will provide emergency outflow of water.