What Is an Artesian Well? How It Works and How It Is Built

An artesian well is a well drilled into a confined aquifer, a layer of water trapped under pressure between two layers of rock or clay. Because the water is under pressure, it rises up the well on its own. If the pressure is strong enough to push water above the ground, it is called a flowing artesian well.

Below we explain how artesian wells work, the two types, how the pipes and casing are set up, how they compare with an ordinary borehole and the problems to watch for. We drill boreholes across Kenya, so the advice comes from real sites.

What Is an Artesian Well?

Most groundwater sits in an open, or unconfined, aquifer. Water there is at normal air pressure, so it only rises to the water table and a pump must lift it the rest of the way.

An artesian well is different. It taps water that is sealed in by an impermeable layer above and below. That water entered the ground on higher land, often many kilometres away, and the weight of the water uphill keeps it pressurised. When a drill breaks through the top seal, the pressure pushes the water up the hole.

Three things are needed for an artesian well:

1. A confined aquifer, such as sand, gravel or fractured rock that holds water.
2. Seals above and below, usually clay or solid rock that water cannot pass through easily.
3. A recharge area on higher ground, where rain soaks in and feeds the aquifer. The height difference creates the pressure.

How Does an Artesian Well Work?

Think of a garden hose running down a hill. If you hold the top end up high and pinch the lower end, the water pushes hard against your thumb. Open your thumb and it squirts out. A confined aquifer behaves the same way: the recharge area is the high end of the hose and the well is the opening.

Hydrogeologists describe the pressure with the potentiometric surface, the level the water would rise to in a well. When that level sits above the ground, the well flows by itself. When it sits below the ground but above the top of the aquifer, the water rises part of the way and a pump does the rest.

Flowing and Non Flowing Artesian Wells

	Flowing artesian well	Non flowing artesian well
Water level	Above the ground	Below the ground, above the aquifer
Pump needed	No, water flows out	Yes, but a smaller lift
Main risk	Uncontrolled flow and wasted water	Pressure falling if over pumped
Wellhead	Valve or cap to control flow	Normal pump and sanitary seal

Non flowing artesian wells are far more common. They still save money, because the water stands higher in the hole and the pump can be set shallower and run with less power.

Artesian Well Pipes, Casing and Flow Control

Pressure is what makes an artesian well useful, and it is also what makes it tricky to build. The pipes have to hold that pressure and stop water escaping around the outside of the casing.

• Casing: a solid pipe, usually PVC or steel, runs from the surface down to the top of the aquifer. Deep or high pressure wells often use steel. See our guide to PVC vs steel borehole casing.
• Grout seal: cement or bentonite is pumped into the gap between the casing and the rock. Without it, pressurised water can leak up the outside of the pipe, soften the ground and even wash out the area around the wellhead.
• Screen: a slotted section sits in the aquifer to let water in and keep sand out.
• Wellhead valve or cap: a flowing well needs a gate valve or a pressure cap so the flow can be shut off when water is not needed.
• Pipe to storage: many owners run the flow into a tank so it can be used later. A raised tank or water tower lets gravity do the work.

Drillers also watch for pressure while drilling. If a strong flow is hit before the casing is ready, the hole can become hard to control, which is why the driller needs to know about artesian conditions in advance. A hydrogeological survey shows this before any rig arrives.

Artesian Well vs a Regular Borehole

	Artesian well	Regular borehole
Aquifer	Confined, under pressure	Usually unconfined or weakly confined
Water level in the hole	High, sometimes above ground	At or below the water table
Pumping cost	Low or none	Normal pump running costs
Construction	Needs full grouting and flow control	Standard casing and sanitary seal
Water quality	Often good, protected by the seal above	Varies with depth and nearby pollution

Both are drilled the same way. The difference is the ground they reach, which is why you cannot simply choose to have an artesian well. It depends on the geology under your land.

Benefits of an Artesian Well

• Lower energy bills: a flowing well needs no pump, and a non flowing one needs a smaller lift.
• Protected water: the clay or rock seal above the aquifer helps keep out pollution from the surface.
• Steady supply: confined aquifers are fed from a wide area, so they often hold up better in dry seasons than shallow wells.
• Fewer moving parts: with little or no pumping, there is less to wear out.

Problems to Watch For

• Uncontrolled flow: a flowing well left open wastes water day and night and can flood the site. Always fit a valve.
• Falling pressure: when many wells draw on the same aquifer, the pressure drops. A well that once flowed may later need a pump.
• Leaks around the casing: poor grouting lets water escape outside the pipe and can let surface water in.
• Natural minerals: deep water can carry iron, fluoride or salt. Test the water before drinking it.

Can You Drill an Artesian Well in Kenya?

Yes, in places where the geology allows it. Artesian conditions are found where layers of clay or volcanic rock seal water bearing beds that are fed from higher ground. We cover where this happens in our guide to artesian wells in Kenya.

An artesian well is a borehole in law, so the usual approvals apply. You need a survey and a permit from the Water Resources Authority before drilling. Our borehole permit guide explains the steps.

How an Artesian Well Is Drilled and Maintained

1. Survey: a hydrogeologist finds the confined aquifer, its depth and the likely pressure.
2. Drilling: the rig drills through the upper seal with the casing and grout ready to go.
3. Casing and grouting: the casing is set and the outside gap is sealed so water rises only inside the pipe.
4. Test pumping: a pumping test measures how much water the well can give without losing pressure.
5. Wellhead: a valve or pump is fitted, along with a pipe to storage.
6. Upkeep: test the water once a year, check the valve and wellhead for leaks and record the flow or water level so you notice any drop early. Our borehole maintenance schedule covers the rest.

Frequently Asked Questions

Is artesian well water safe to drink?

It is often cleaner than shallow well water because the aquifer is sealed from the surface. It can still carry natural minerals or be polluted by a poor wellhead, so test it before drinking.

Does an artesian well ever stop flowing?

It can. If the aquifer is overused or a long drought cuts recharge, the pressure falls. The well may then need a pump even though it once flowed freely.

How deep is an artesian well?

There is no fixed depth. It depends on how deep the confined aquifer lies, which can be tens of metres or several hundred. A survey gives the expected depth for your site.

Is an artesian well the same as a spring?

No. A spring is where groundwater reaches the surface naturally. An artesian well is drilled, and the pressure in the aquifer pushes water up the hole.

Thinking About a Borehole?

Whether your site turns out to be artesian or not, the first step is the same: a survey that shows where to drill and how deep. Call or WhatsApp Bonvic Drilling on 0727 666 444 or send us your location, and use our borehole cost calculator to plan your budget.