The answer to how does a well work is shorter than most people expect: a lined hole reaches water that is already sitting in the ground, a pump lifts it, and a tank in the basement holds it under pressure until you open a tap.
Each of those parts has a job, and each one has a way of failing that you can learn to recognise. On our builds, the well is part of site preparation, which I oversee along with excavation and foundations. Here is the whole path, from the water underground to your kitchen, and what keeps it working.
How does a well work? It starts with water already in the ground
A well does not make water. It reaches water that is already there.
Below a certain depth, the spaces between grains of sand and gravel, or the cracks in solid rock, are full of water. The top of that saturated zone is the water table. A layer that holds enough water and gives it up readily enough to supply a well is an aquifer. Rain and snowmelt soaking down from the surface keep refilling it, a process called recharge.
When a well is not being pumped, the water inside it settles at a level called the static water level. Every other part of the system is built around that number: how deep the pump hangs, which kind of pump suits the well, and how much water you can draw before the level falls too far.
How does a well work below ground? The casing and the seal
The hole itself is only half the well. What keeps the water clean is the lining and the seal around it.
- The casing is the pipe that supports the sides of the hole. Where the useful water is more than 6 metres down, Ontario’s Wells Regulation requires the casing to reach at least 6 metres below the original ground. Where it ends in solid, unweathered rock, it has to be sealed into the rock.
- The seal fills the gap between the outside of the casing and the wall of the hole. Without it, surface water could run straight down the outside of the pipe and into the water you drink. The regulation requires that gap sealed against water, gas and contaminants moving between layers or from the surface.
- The screen sits at the bottom where the water comes in. In sand and gravel it filters out particles and keeps the ground from collapsing into the well. In rock, the hole below the casing often stands open on its own, so a screen is only sometimes needed.
Above ground, you see very little of all this: a casing standing at least 40 centimetres above the ground around it, a vermin-proof cap on top, and a well tag fixed to the pipe. The ground is mounded so water runs away from the casing rather than pooling against it.
A new well has to be at least 6 metres deep unless the only usable water is shallower, and then it still has to reach 3 metres. Our post on dug versus drilled wells covers how the two main kinds are built and why the deeper, sealed kind is harder to contaminate.
The pump: pushing from below or pulling from above
Water does not climb a casing on its own. Something has to lift it, and in most homes that is one of two kinds of pump.
Submersible pumps
A submersible pump hangs inside the well, below the water, on a single drop pipe. Because it pushes water up rather than drawing it, it works at almost any depth a house will need; the province lists them as capable to about 305 metres (1,000 feet). It runs quietly, it is unlikely to freeze down there, and its control box sits inside the house. It needs a well at least 10 centimetres (4 inches) across.
The trade-offs: pulling it out for service is more work than reaching a pump in the basement, sand in the water wears its parts, and a lightning strike can take it out.
Jet pumps
A jet pump sits in the basement or a pump room and pulls water up. A shallow-well jet pump works to about 7.6 metres (25 feet). A deep-well jet pump uses two pipes down the well and reaches about 30 metres (100 feet), or further with multi-stage units. Jet pumps cost less and are easy to reach, but they can be noisy, they struggle with sandy water, and a small leak in the line can stop them priming.
Whichever pump is used, a valve at the bottom of the line, called a foot valve or check valve, keeps the water in the pipe from draining back down the well each time the pump stops.
The pitless adapter keeps the line below the frost
Somewhere between the well and the house, the water has to turn sideways and travel underground. In Central Ontario that turn has to happen below the frost line, or the line freezes.
The fitting that makes the turn is the pitless adapter, usually brass, mounted through the side of the casing below the frost line. Inside the well, it connects to the drop pipe. Outside, it connects to the buried line running to the house, so no pipe is ever exposed above ground. It has to be watertight to the casing, because a leaky joint below ground is an open door for surface water. It replaced the old well pits and pump houses that used to keep this connection from freezing.
The buried line then enters the basement below the frost line and is sealed where it passes through the foundation wall. On a submersible system, the pump’s power cable runs the same way, out to the well and down to the pump.
The pressure tank is why the tap does not wait
If the pump had to start every time you opened a tap, it would be switching on and off all day. The pressure tank is the answer, and the province’s guide lists one as a requirement for both kinds of pump above.
The tank sits in the basement and holds a store of water under pressure. When you open a tap, that pressure pushes water out. As the tank empties and the pressure drops, the pump starts and refills it. Then it stops again, and the tank carries the house until the next cycle.
Some systems use a variable-speed pump that keeps the pressure constant rather than letting it rise and fall. Those systems get by with a much smaller tank, which saves space in a mechanical room.
How does a well work when the power goes out?
It mostly does not. The pump runs on electricity, so once the power is gone, the only water left under pressure is whatever is in the tank. On a constant-pressure system with a small tank, the province says plainly that there is very little water available during an outage. If outages are common on your road, that is worth thinking about when the mechanical room is being planned, not after the first storm.
How much water a well can give
The question most people actually mean when they ask how a well works is: will it keep up? The yield test is how a contractor answers it.
When a well is finished, the contractor measures the static water level, then pumps the well at a steady rate for at least an hour. The drop in the water level while pumping is the drawdown. When the pump stops, they keep measuring for at least another hour as the level recovers. A well that recovers quickly at a good pumping rate is drawing on plenty of water. A well whose level keeps falling is telling you something about the ground it sits in.
Ontario does not set a minimum yield for a house. The test is there to inform you, the owner, about the rate the well can sustain. The results, along with the recommended pump depth and pumping rate, go on the well record you are given when the well is finished. Keep it, because the next person to work on your pump will want it.
How does a well work over the years? Keeping it working
A well that was built properly asks for very little, but it does ask. The province’s own advice for owners is short and practical:
- Test the water at least three times a year, including every spring and fall, and more often if anything changes. Public Health Ontario supplies free kits for bacterial testing; chemical testing goes through a licensed lab for a fee.
- Watch for changes in colour, taste or smell.
- Look at the top of the well. The cap should be secure, and the casing free of rust, cracks, holes or gaps that would let in insects, mice or surface water.
- Keep the area clear. No ponded water, parked vehicles, pet waste, salt or fertilizer near the well, and the ground sloping away from it.
- Listen to the pump. New or unusual sounds can mean wear on the pump, the lines or the electrical cable.
- Notice a pump that runs and runs, or pressure that keeps dropping. That can point to a crack or hole in a waterline.
- Look after the septic system. A septic tank has to sit at least 15 metres from a well, and the bed’s pipes 15 or 30 metres depending on how the well is cased.
Keep the well reachable, too. A casing buried under a new garden bed or a deck is a casing nobody can service without tearing something up.
Where to start
If you are planning a build on a rural lot, the well is one of the first things decided and one of the last things you think about once it works. On our projects, well drilling is handled as part of site preparation, together with the septic system, the driveway and the grading, so the pieces are placed with each other in mind. If you want to understand the cost side before you start, our post on the price to drill a well walks through what a quote pays for.
If you are looking at a lot and want to talk through what it needs, tell us about the property. We reply within two business days.
Frequently Asked Questions
How does a well work without electricity?
The pump needs power, so during an outage you have only the water already stored under pressure in the tank. A conventional pressure tank gives you a little; a constant-pressure system with a small tank gives you very little.
How deep does a well have to be in Ontario?
Under Ontario’s Wells Regulation, a new well must be at least 6 metres deep unless the only usable water is shallower, in which case it must still be at least 3 metres deep. Where the water is deeper than 6 metres, the casing has to reach at least 6 metres down.
What is the difference between a submersible pump and a jet pump?
A submersible pump hangs in the well below the water and pushes water up; it suits deep wells, runs quietly and is unlikely to freeze. A jet pump sits in the house and pulls water up; it is cheaper and easier to reach, but limited to about 7.6 metres for a shallow-well model and about 30 metres for a deep-well model.
What does a well pressure tank do?
It stores water under pressure so a tap can run without the pump starting every time. When the tank’s pressure drops, the pump starts and refills it, then shuts off again.
How often should I test my well water?
The province recommends at least three times a year, including every spring and fall, and more often if you suspect a problem. Public Health Ontario provides free kits for bacterial testing.
