Groundwater is extracted primarily by drilling wells into underground aquifers and pumping water to the surface. This single method, in various forms, supplies about 50 percent of the world’s domestic drinking water and over 40 percent of irrigation water. The process involves drilling through soil and rock to reach saturated zones, installing a sealed well structure, and using mechanical pumps to bring water up.
How Water Moves From Rock to Well
Underground, water fills the tiny gaps and fractures in soil, gravel, and rock formations called aquifers. Below a certain depth, known as the water table, every opening in the rock is completely saturated. When a well is drilled into this saturated zone, water naturally rises in the borehole to roughly the level of the water table, the same way water finds its level in a connected container.
Pumping water out of the well creates a pressure difference. Gravity and hydraulic pressure force surrounding groundwater to flow through the rock toward the well, replacing what was removed. This movement creates a funnel-shaped dip in the water table around the well, called a cone of depression, with its lowest point at the well itself. The size and shape of this cone depend on how fast water is pumped, how long pumping continues, and how easily water moves through the surrounding rock. In pressurized (artesian) aquifers, the cone spreads rapidly and the well can draw water from a wide area. In other aquifers, the effect is more localized but can still lower water levels several miles from the well over years of steady pumping.
How Wells Are Drilled
Two main drilling methods dominate the industry. Rotary drilling uses a spinning drill bit, sometimes combined with a hammering action, to bore through rock. Several variations exist: air-rotary, mud-rotary, and downhole hammer rigs. These are powerful enough to drill over 300 feet through bedrock in a single day, making them the standard choice for most modern wells.
Percussion drilling, also called cable tool drilling, is one of the oldest techniques, developed in China over 4,000 years ago. It works by repeatedly raising and dropping a heavy drill stem into the ground, chipping away at rock with each blow. It’s far slower than rotary drilling but remains common in some regions because the equipment is simpler, cheaper, and easier to maintain.
In the United States, the median depth for a domestic well is about 142 feet, while public supply wells typically go deeper, with a median around 202 feet. Some wells in arid regions or areas with deep aquifers extend much further.
Parts of a Modern Well
A finished well is more than just a hole in the ground. Each component serves a specific function to keep water clean and flowing reliably:
- Casing: A tube, usually steel or PVC, that lines the borehole from the surface down to the water-bearing zone. Sealed with grout on the outside, it prevents dirt and contaminated surface water from seeping in and mixing with drinking water.
- Well screen: A filtered section attached to the bottom of the casing that allows water in while blocking sand and sediment.
- Well cap: A sealed cover on top of the casing that keeps out debris, insects, and animals. It includes a small vent to equalize pressure during pumping.
- Pitless adapter: A fitting that connects the water pipe to the casing below the frost line, preventing the connection from freezing in cold climates while maintaining a sanitary seal.
Pump Types and Depth Ranges
The type of pump you need depends almost entirely on how deep your water sits. Two designs handle the vast majority of residential and agricultural wells.
Jet pumps sit above ground and pull water up using suction. Shallow-well jet pumps use a single pipe and work best when the water level is within about 25 feet of the surface. Deep-well jet pumps use two pipes, one sending pressurized water down and another bringing water back up, and can reach depths of roughly 50 to 90 feet. Because suction has physical limits, jet pumps aren’t practical for very deep wells. They do require priming, produce audible noise, and are exposed to weather.
Submersible pumps are installed inside the well casing itself, sitting below the water line. Instead of pulling water up with suction, they push it upward with pressure. This makes them effective for wells over 100 feet deep and the standard choice for most deep private wells. They run silently at the surface, don’t need priming, and aren’t exposed to weather. The tradeoff is that repairs require pulling the entire pump assembly out of the well.
Boosting a Low-Yield Well
Sometimes a newly drilled well doesn’t produce enough water, or an older well gradually loses flow as minerals build up in the rock fractures that feed it. Two development techniques can improve production.
Hydrofracturing, used commonly in the water well industry since the 1990s, involves sealing off a section of the well with an inflatable plug and injecting clean water under high pressure, typically between 500 and 3,500 pounds per square inch. Since water can’t be compressed, this force pushes outward against the borehole walls, flushing fine particles from existing fractures and widening them. The process is usually repeated at several depths within the same well, with 1,000 to 2,000 gallons of water pumped into the formation across multiple sessions.
Surging is a simpler, less common method. A heavy weight is repeatedly raised and dropped inside the well, creating a rhythmic push-pull action that flushes debris from fractures. It’s gentler than hydrofracturing but can still meaningfully improve water flow in bedrock wells.
Solar-Powered Extraction
In remote locations without reliable electricity, solar-powered pumping systems offer a practical alternative. A basic setup includes a photovoltaic (PV) array, a pump controller that matches electrical output to the pump’s needs, a DC pump designed for solar efficiency, a storage tank, and a float switch to prevent overflow or dry pumping.
One significant advantage for agricultural use is portability. The solar array can be trailer-mounted and moved between sites as needed. Adding a solar tracking device, which tilts the panels to follow the sun, can increase daily energy output by up to 40 percent at certain latitudes. Deep-cycle lead-acid batteries provide backup power for cloudy days or nighttime operation, charged during the day through the PV array and regulated by a charge controller to prevent overcharging.
What Happens When Too Much Is Extracted
Groundwater is renewable, but only up to a point. When pumping consistently exceeds the rate at which rain and surface water recharge an aquifer, problems follow. The water table drops, the cone of depression around each well deepens and widens, and wells that were once productive can go dry. Over 40 percent of the world’s irrigation water now comes from aquifers that are being steadily drained.
In coastal areas, overpumping creates a particularly damaging problem called saltwater intrusion. Freshwater in coastal aquifers normally holds back denser saltwater from the ocean. When pumping lowers freshwater levels, that balance shifts and saltwater migrates inland, both laterally from the coast and vertically upward near pumping wells. Once saltwater contaminates a well, the water becomes unusable, and in extreme cases entire well fields have been abandoned. The contamination can persist long after pumping stops, since flushing salt from an aquifer is extremely slow.
Land subsidence is another consequence. As water is removed from the pore spaces in clay and silt layers, the ground above can compact and sink permanently. This is irreversible: once the structure of the aquifer compresses, it loses storage capacity and can never hold as much water again, even if levels are later restored.