A water well is a structure built to access groundwater, the water stored beneath the Earth’s surface. Constructing a successful well relies on geology and physics to locate and draw this resource. The well is created by drilling a hole deep enough to reach a water-saturated rock or sediment layer. Once reached, the well provides a reliable pathway for the water to be mechanically brought to the surface for home, agriculture, or industry use.
The Source: Understanding Groundwater and Aquifers
Groundwater originates from precipitation that soaks into the ground and filters downward through the soil and rock layers. This water continues to move down until it reaches the zone of saturation, where all the open spaces in the geologic material are completely filled with water. The upper surface of this zone of saturation is known as the water table, which rises or falls depending on the amount of rainfall and the rate of pumping.
A geologic formation that can store and transmit a usable quantity of water is called an aquifer. The ability of a material to hold water is its porosity, measured by the percentage of open space within the rock or sediment. Permeability is the measure of how easily water can flow through that material, which depends on how well the pores are connected.
Aquifers are generally categorized as unconfined or confined. An unconfined aquifer has the water table as its upper boundary, meaning it is in direct contact with the atmosphere through the soil above it. Conversely, a confined aquifer is sandwiched between layers of low-permeability material, often called aquitards or aquicludes, which restrict the flow of water. Wells are specifically designed to penetrate these layers and tap into the water-bearing formations below.
Different Types of Water Wells
Water wells are categorized into three main types based on construction method and depth.
Dug Wells
Dug wells are the oldest method, historically excavated by hand or with a backhoe. These wells are shallow, typically 10 to 50 feet deep, and have a wide diameter. Drawing water from near the surface makes them highly susceptible to contamination from surface runoff and prone to running dry during drought.
Driven Wells
Driven wells are an intermediate depth option, constructed by driving a small-diameter pipe into the ground. They are effective in areas with unconsolidated materials like sand and gravel and a high water table. Driven wells reach depths between 30 and 50 feet. While economical, their shallow nature makes them vulnerable to contamination and seasonal water level fluctuations.
Drilled Wells
Drilled wells are the most common and modern type, created using specialized rotary or percussion drilling machines. This method allows the well to reach hundreds or even over a thousand feet deep, tapping into reliable, deep confined aquifers. Their depth and continuous casing installation offer the best protection against surface contamination and provide a consistent water supply.
Anatomy and Extraction Mechanism
The structure of a modern well maintains access to the aquifer and protects water quality. The well casing is a tube, typically steel or PVC, placed in the borehole to prevent collapse. It also acts as a sanitary seal, working with an outer layer of grout to block contaminants from seeping down the outside of the well bore.
At the bottom of the casing, within the aquifer, is the well screen. This screen acts as a sieve, allowing groundwater to flow into the well while filtering out sand, gravel, and sediment that could damage the pump. The water inside the casing must then be lifted to the surface using a pump system.
Jet Pumps
The most common methods for lifting the water involve either a jet pump or a submersible pump. A jet pump is mounted above ground and uses centrifugal force to create suction, pulling the water up. Jet pumps are limited in their effective suction, working best for shallow wells less than 25 feet deep.
Submersible Pumps
Submersible pumps are placed entirely underwater, deep within the well casing. This design allows the pump to push water up the pipe, overcoming the suction limitations of jet pumps. Submersible pumps are more efficient and capable of delivering consistent flow and pressure from depths exceeding 1,000 feet, making them the preferred choice for deep drilled wells.