How Does a Water Well Work?
A well system consists of the well itself, which is inside a casing, a jet pump -- possibly a submersible pump -- and a pressure tank.
Water wells are as old as civilization -- maybe older -- but modern rural dwellers who rely on drawing groundwater for their water needs don't have to use buckets or hand pumps like their forebears. Modern well systems still employ pumps -- electric ones -- but it takes more than a pump to get water from the ground to your kitchen faucet. If you have a well system, it's good to understand how it works so you can give it the maintenance it needs.
Accessing the Water
The type of well system you have depends to a large extent on how high the water table is in your area. Virtually all modern wells are drilled; surface water is too vulnerable to contamination to be reliable. Wells can be anywhere from 15 to several hundred feet deep, depending on the topography and height of the water table. Drilling methods include:
- Cable tool -- A chisel like tool attached to a cable is repeatedly lowered, breaking rock into small chunks that are removed with a bailer.
- Rotary method -- A drill rod with a rotating bit is gradually lowered into the ground. A water/clay mixture, forced through the drilling point, carries dirt and rocks to the surface as the bit digs.
- Drive point -- A series of interconnected pipes are driven into the ground. When the tip of the lowest pipe, which is covered with a pointed screen, enters the water table, water begins flowing into the pipe.
- Auger method -- An earth auger bores a hole in the ground, and the hole is lined with concrete or some other casing material.
The auger and drive-point methods are used mainly for wells less than 50 feet deep, and together with the method of manually digging down to the water table with a shovel, aren't considered acceptable methods in some states, such as Minnesota.
Components of a Well System
Once the well has been dug, it's lined with a casing, which is usually 4- to 6-inch PVC pipe. The casing provides a pathway for transporting water to the surface, and it often houses the pump. There is usually a well screen on the end of the casing to filter out rocks and sediment. The space between the casing and the sides of the hole is usually filled with grout, a mixture of water and cement.
Shallow wells employ a jet pump that's usually located in a well house or in the basement. Jet pumps function by creating a vacuum that sucks water out of the ground. Deeper wells usually have a submersible pump housed inside the well casing, and it connects to power by insulated wires. Unlike jet pumps, submersible pumps push water through the pipes. A foot valve -- which is a type of check valve -- in the well casing prevents water from falling back into the well once it has been pumped up.
The pitless adapter is a plumbing fitting that connects the well casing to the water supply pipes that lead to the pressure tank. The actual connection is below the frost line, and the top of the pitless adapter extends to ground level. It has a removable cap that allows access to the well casing.
The pressure tank -- a water storage tank -- has an air cavity and a rubber bladder to keep the air and water separate. The purpose of the bladder and air cavity is to keep water pressurized so the pump doesn't have to come on every time you need water.
Wells with a submersible pump usually have a separate jet pump to pressurize the tank, and the jet pump on shallow well systems does this automatically. A pressure-sensitive switch monitors the pressure in the tank and switches the pump on when the pressure falls below the switch's cut-in value. It switches the pump off when the pressure reaches the cut-out value. This switch has an adjustment screw that allows you to adjust cut-in and cut-out pressure together, and another one for adjusting just the cut-out pressure. Properly adjusting the switch extends the life of the pressure pump and -- if there is a separate one -- the well pump.