- When you turn the water on, it flows from the tap or the showerhead because of water pressure and gravity (a cubic foot of water weighs about 62 lbs). Water utilities and well drillers use two methods of creating enough water pressure to push water into all the spigots served by their district. One way harnesses gravity and the other uses a rule of physics--Boyle's law--to push the water.
- When you raise a few hundred cubic feet of water in the air, it takes a great deal of strength to keep it there. If you built a stout 50-foot tower out of steel and concrete, put 1,000-gallon or more tank atop it and pump it full of water, the downward force will total more than 4 tons. A series of pipes and pumps located beneath the tower can easily transport water anywhere located beneath the tower. The challenge of a supply system design is to deliver water to all users at a fairly uniform pressure of 30 to 50 lbs. per square inch (psi). The consumers nearest the water tower will have higher water pressure, and those who live farther away or at higher elevations will notice lower water pressure, particularly during high-use times. In order to manage flow, utilities install systems that drop as they get farther from the center, vary pipe sizes and employ "lifts" to change elevation. Control valves are installed to direct flow in volume proportionate to use and there's no avoiding the need for pumps to assist some movement patterns. Users who habitually have too much or too little pressure in their homes or businesses may need to involve flow controls or pumps to protect their plumbing from "knocks" and damage. The main tank will have to be filled from time to time of course; if the community is fortunate enough to have an artesian well, engineers can use naturally occurring water pressure to augment pumps.
- In areas where the use of gravity needs some help, or a gravity tank is not practical, water utilities use pressure tanks that operate by pumping water into a sealed tank through a bladder that compresses the air in the tank until it presses back on the water with enough force to move the water as far as it needs to go. Pressure is maintained in the tank by replacing water in the tank when the air reaches a minimum or negative pressure. Although this concept, called Boyle's Law, considers other variables, such as air temperature and elevation, the basic idea is to use the air to move the water.
