A well is a pipe reaching down into the water in the ground. Its trick is at the bottom: a slotted screen and a ring of gravel that let water in but keep sand out. Use the buttons to look inside and follow the water from the aquifer up to the surface.
A groundwater well is a drilled hole, lined with a casing pipe, that reaches down into the water held in the ground. Its purpose is to bring that water to the surface cleanly, without pulling up the sand it is sitting in. The clever parts — the screen and the gravel pack — are all at the bottom, underground.
From the surface a well looks like a pipe with a cap. What matters is buried far below: where it meets the water, how it lets water in, and how it keeps sand out. Cutting it open shows how a slotted screen and a carefully graded gravel ring work together to turn a muddy aquifer into a source of clear water.
Below the water table the ground is a layer of sand and gravel with water filling all the spaces between the grains. This layer is the aquifer, and it is the source the well is drilled to reach.
Around the screen the gap is backfilled with a ring of coarse gravel, the filter pack. As water seeps toward the well it passes through this gravel, which traps the fine sand and silt so they do not travel on and choke the well.
The lowest part of the casing is the screen, a pipe with narrow slots. The openings are wide enough for water to flow through, but too narrow for the gravel and coarse sand to pass, so the well fills with water and not sediment.
Inside the casing a drop pipe runs from the pump up to the surface. Water that has entered the well gathers at the bottom, and the drop pipe is the passage it uses to travel up to the well head.
Sitting low in the well, below the water line, a submersible pump does the lifting. It pushes the water up the drop pipe continuously, which is why a well can supply water faster than it would simply rise on its own.
Near the top a grout seal fills the space between the casing and the borehole, and a cap closes the well head. Together they stop rain and surface water running down the outside of the casing and contaminating the supply.
The screen is the slotted section at the bottom of the casing. It has openings wide enough to let water in but narrow enough to hold back sand and gravel, so the well fills with clean water instead of being buried in sediment.
It is a filter pack. Coarse gravel is placed in the ring around the screen so that fine sand from the aquifer is trapped there, before it can clog the opening or be pulled into the pump.
A grout seal. It fills the gap between the casing and the borehole near the top, so rain and surface water cannot run straight down the outside of the casing and contaminate the well.
A submersible pump sits low in the well, under water. It pushes water up a drop pipe to the well head at the surface, where it leaves through the pipework.
From the aquifer, a layer of water-bearing sand or gravel below the water table. The well simply reaches down into it and lets water flow in through the screen.