Re: What are the advantages/disadvantages of using water towers?

You are correct. There are energy losses in pumping water to the top of a water tower just to send it back down. Although the potential (elevation) energy is more or less a wash, there are significant losses in pipe friction. That, and the liability/security issues, are major disadvantages of water towers.

As for the advantages; it is very difficult to maintain a constant water pressure with pumps throughout changes in water demand. A tower provides stable pressures throughout the system, and provides a reservoir of water to accommodate surges in demand. However, even if the water level in the tower is assumed constant (static pressure fluctuations are usually pretty small compared to the overall height of the tower), the energy losses within the distribution system increase with the square of the demand flow velocity. That usually means that we are going to notice a corresponding drop in line pressure with increases in public demand, no matter what we do. There is no perfect system. We strive to design appliances that can operate within a broad window of line pressures. If we cannot accommodate the fluctuations in the public delivery pressures, we must provide our own booster pressure.

You could pump against a flexible bladder, or against an air pressure, but these systems do not contain sufficient volume to provide demand surge capacity. The water tower itself is under relatively little pressure; much less than the static line pressure at ground level. Water towers can be filled at a time of day when electrical power is cheaper. They can be filled at a steady rate throughout the day, to optimize the efficiency of the pumps and minimize friction losses (remember: four times the flow rate means sixteen times the friction loss). And, in the case of a power loss or pump failure, the public delivery system runs independent of the pumps (until the tank is empty).