Well pump and pressure tank field guide for private water systems

A well system and its four parts

A private well water system does four jobs with four parts. The well is the hole that reaches groundwater. The pump lifts that water out of the ground and pushes it into the building. The pressure tank stores a few gallons under pressure so the pump does not have to start every time someone opens a tap. The pressure switch watches the pressure and tells the pump when to run and when to stop. Take any one of the four out of the picture and the other three do not work right.

The difference from city water is that you own the whole supply. On a municipal system the utility delivers water to your meter at a pressure it holds, and the pipe sizing inside the building is the whole plumbing problem, which is its own work covered in the water supply pipe sizing guide. On a well, you are the utility. You make the pressure, you store it, you protect the source, and you fix it at 2 a.m. when the pump quits. Everything downstream of the tank is ordinary plumbing. Everything from the tank back to the aquifer is yours.

Most of what goes wrong on these systems is not the pump dying on its own. It is the tank or the switch driving the pump into a failure, and then the pump gets blamed and replaced while the real fault sits there waiting to kill the new one. That pattern is the through-line of this guide.

The well itself: casing, water levels, and yield

Wells come in three rough types. A drilled well is a small-diameter bore, commonly 4 to 8 inches across, sunk by a rig tens to hundreds of feet into rock or sand, lined with a steel or plastic casing, and it is what almost every modern system sits on. A bored or dug well is wide and shallow, a few feet across and rarely more than 30 to 40 ft deep, the old farm style, and it leans on a high water table. A driven-point well is a pipe with a screened point hammered into shallow sand. The type sets which pump you can use before anything else does.

Three numbers describe how a well behaves. Static water level is where the water stands in the casing with the pump off, the top of the water column at rest. Pumping level, sometimes called the drawdown level, is where the water falls to while the pump runs. The gap between them is the drawdown. Specific capacity ties it together: gallons per minute of yield per foot of drawdown, so a well that gives 10 gpm at 10 ft of drawdown has a specific capacity of 1 gpm per foot.

Yield is the number that governs the whole design. It is how many gallons per minute the aquifer will actually give up over a sustained pump run, and it is not the same as how much the pump can move. A well that recovers at 5 gpm cannot feed a 12 gpm pump no matter how big the pump is. You will pull the level down to the intake and start sucking air. The tested yield, measured at drilling or supplied on the well log, is the ceiling every other decision lives under.

Submersible pumps: the deep-well standard

A submersible pump sits down in the well, below the water, and pushes water up the drop pipe to the surface. The motor and the pump are one sealed cylinder, long and narrow to fit a 4 inch casing, hung on the drop pipe with the power cable strapped alongside. It pushes from below rather than pulling from above, which is why it reaches deep wells a surface pump cannot touch. Most new installations on a drilled well are submersible, and they run from shallow sets down to 300 ft and beyond.

The pump is multi-stage. Each stage is an impeller and a diffuser, and they stack in series so each one adds to the head, the vertical lift plus pressure the pump can make. More stages, more head. That stacking is how a unit a few inches across lifts water from 200 or 300 ft down and still delivers usable pressure at the top.

Submersibles come in 2-wire and 3-wire versions, and the difference matters at install and at troubleshooting. A 2-wire pump has its starting components built into the motor down in the well, so there is no control box up top. A 3-wire pump puts the start capacitor and relay in a control box at the surface, which makes those parts reachable but adds a piece that can fail. When a 3-wire pump hums but will not start, the control box is the first thing to check, because a failed start capacitor is cheaper and more common than a dead motor 250 ft down.

Jet pumps: shallow-well suction and the deep-well two-pipe

A jet pump sits above ground and pulls water up by suction, and that is its limit and its character. Suction lift is capped by atmospheric pressure at a theoretical 33 ft and a practical 25 ft or so at sea level, less at altitude. A shallow-well jet pump, single pipe, works only where the water level stays within about 25 ft of the pump. Past that the suction runs out of physics, not out of horsepower.

To go deeper, a deep-well jet pump uses two pipes and an ejector, also called a jet assembly, down in the well. The pump sends pressurized water down one pipe to the ejector, where a nozzle and venturi create suction at depth, and the combined flow comes back up the second pipe. Recirculating water to make suction at the bottom is what lets a surface pump reach water 80 to 100 ft down. A convertible jet pump is the same surface unit set up for either job, shallow with a single pipe or deep with the ejector kit, commonly rated to about 90 ft.

Jet pumps are the older technology and they convert a smaller share of motor power into water movement than a submersible. They are noisier, they sit in the basement or the well house where you hear them run, and they have to be primed and hold prime to work at all. The reason to choose one is depth and budget, which is the next decision.

Submersible or jet pump: which do I need?

Depth decides it. If the water is more than about 25 ft below the pump, a shallow-well jet is out, and on most drilled wells a submersible is the right call. The submersible runs more efficiently, sits quiet underground, holds prime because it is already underwater, and lasts longer because it runs cool surrounded by the water it pumps. For a deep drilled well it is the default, and the trade has moved that way for decades.

The jet pump earns its place in two cases. One is a genuinely shallow source, a dug or bored well or a high water table within suction reach, where a single-pipe shallow jet is cheap and easy to service from above. The other is an existing deep-well jet system that still works, where converting to submersible means pulling pipe and rewiring, and the cost does not always favor the change.

The honest version: on a new deep well, install a submersible. On a shallow source, a jet is fine and often cheaper. The deep-well two-pipe jet is mostly a legacy system you maintain rather than a thing you install new, because a submersible does the same depth with less power and less noise. Match the pump to the well first, then size it, and let the well yield cap both.

How does a well pressure tank work?

A well pressure tank stores water under pressure using a cushion of trapped air, so the pump does not have to run every time you open a faucet. Most modern tanks are bladder or diaphragm type: a sealed rubber bladder holds the water on one side and a charge of compressed air sits on the other. As the pump fills the tank, water compresses the air. As you draw water, the compressed air pushes it back out at pressure. The air is the spring.

The useful number is drawdown, the gallons of water the tank actually delivers between cut-out pressure, when the pump stops, and cut-in pressure, when the pump starts again. Drawdown is not the tank's total volume. A 44 gallon tank might give 10 to 14 gallons of real drawdown depending on the pressure settings and the pre-charge. The bigger the drawdown, the longer the pump rests between runs.

That rest is the whole point. Without a tank, or with a dead one, the pump starts the instant you crack a tap and stops the instant you close it, hammering itself on and off. The tank turns dozens of short pump starts into one longer run by storing a buffer the building draws from first. A correctly sized and correctly charged tank is the difference between a pump that runs for years and one that burns out in a season.

The air pre-charge: the number-one tank setup

The single setup step people get wrong is the air pre-charge. Set the tank's air pressure to about 2 psi below the pump's cut-in pressure, with the tank empty of water and the pump off, measured at the air valve on top with a tire gauge. On a 30/50 switch, cut-in is 30, so pre-charge to about 28 psi. On a 40/60 switch, pre-charge to about 38 psi. Confirm the exact figure against the tank and switch manufacturer, because some call for a slightly wider gap on higher-pressure systems.

Here is why 2 psi below cut-in. If the pre-charge is too low, the bladder cannot push the last of the water out, the tank delivers less drawdown than its size promises, and the pump cycles more than it should. If the pre-charge is too high, the tank empties before pressure falls to cut-in and you get a dead spot, a moment where the faucet drops to nothing before the pump catches up. Two psi under cut-in empties the tank just as the pump is about to start.

Check it with the tank drained. Air pressure read against a tank full of water tells you nothing, because the water is holding the bladder back. Shut off the pump, open a faucet to bleed the system to zero, then read and adjust the air valve. And if you change the switch settings later, you reset the pre-charge to match. The two numbers are a pair.

What pressure should a well system be set at?

A well system runs between two pressures the switch controls: the cut-in, where the pump turns on, and the cut-out, where it turns off. The two most common factory settings are 30/50 and 40/60 psi, meaning the pump starts at 30 or 40 and stops at 50 or 60. The 20 psi gap between them is the differential, the working band the system cycles across.

Pick the band for the building. A 40/60 switch gives stronger fixture pressure and suits a two-story house or a long run to outbuildings, where 30/50 can feel weak at the upstairs shower. Going higher costs you some tank drawdown and loads the pump and the plumbing harder. Most homes run fine on 30/50 or 40/60. Above 60 is for a specific need, like feeding a system that wants the extra head, not a general default.

Whatever you set, the pre-charge follows it. Change the switch from 30/50 to 40/60 and you have to re-charge the tank from about 28 to about 38 psi, or the tank fights the new band. The switch number and the pre-charge number move together, every time. Set one without the other and you have built in a cycling problem on purpose.

Why does my well pump short cycle?

Short cycling is the pump turning on and off rapidly, every few seconds, instead of running a minute or two and resting. It is the most common well-system failure and the fastest way to destroy a pump. The motor draws its highest current at startup, so a pump that starts over and over overheats, wears the start components, and can drop from a fifteen-year life to a few months. If you hear the pump clicking on and off in quick bursts, shut it off and find the cause before it eats itself.

The number-one cause is a waterlogged tank, a tank that has lost its air charge and filled with water, leaving no air cushion. Service data puts the failed or waterlogged tank behind the large majority of short-cycling calls. With no air spring, the tank holds almost no drawdown, so the pump fills it in seconds, hits cut-out, then falls to cut-in the moment you use any water, again and again.

Diagnose it fast. With the pump off, tap up the side of the tank: a healthy tank rings hollow at the top, where the air is, and dull at the bottom, where the water is. A waterlogged tank sounds dull all the way up. Then push the pin on the air valve on top. Air should hiss out. If water sprays out, the bladder has failed and the tank is done. The fixes, in order of likelihood: a lost pre-charge you can re-pump, a failed bladder that needs a new tank, or a faulty pressure switch chattering on a bad contact or a clogged sensing port.

The controls: switch, control box, and cutoff

Beyond the pressure switch, a well system carries a small set of controls, and which ones you have depends on the pump. The pressure switch is the brain, a pair of contacts that close to run the pump at cut-in and open to stop it at cut-out. It mounts on the tank tee and senses pressure through a small port that can clog with iron or sediment and make the switch read wrong, which is a real and overlooked failure.

A 3-wire submersible adds a control box at the surface, holding the start capacitor and start relay that get the motor spinning. A 2-wire pump has those parts in the motor and needs no box. When a 3-wire pump hums but will not start, or trips its overload, the control box and its capacitor are the first suspects, because they are reachable and they fail more often than the motor.

The control most often missing is a low-pressure cutoff, sometimes built into the switch as a lever marked for it. It opens the circuit if system pressure falls below a set floor, which is what happens when the well runs low and the pump loses its water. Without it, a pump that loses prime or pumps the well down keeps running dry. With it, the pump shuts off and waits, and on most you reset it by hand once the well recovers. That manual reset is the point: it makes you notice the problem instead of cooking the pump quietly.

Constant-pressure and variable-speed systems

A constant-pressure system runs the pump at variable speed instead of flat on or flat off. A variable frequency drive, the VFD, ramps the pump motor up and down to hold a steady delivery pressure as demand changes, so the pressure at the shower stays put whether one tap is open or four. It is the modern upgrade over the cycling on-off system, and on a deep submersible it is a real change in how the water feels at the fixture.

Two practical gains come with it. The pressure tank shrinks, because the drive holds pressure instead of relying on a big stored drawdown, so a constant-pressure system often runs on a small 20 to 30 gallon tank or a tiny one. And the soft start and stop are gentle on the pump and the well, with none of the hard cycling that wears a conventional system. The drive costs more up front and adds electronics that need protection from surge and heat.

The feature that matters most on a marginal well: the drive can be programmed to cap the pump speed at the well's sustainable yield. Set the maximum output to match what the aquifer gives, and the pump physically cannot draw the well down faster than it recovers. On a low-yield well that is the difference between a system that paces itself and one that keeps pumping itself dry.

Sizing the pump to the well yield

You size a well pump to two things at once: the demand the building needs and the yield the well can give, and the smaller of the two wins. Demand comes from the fixtures, the peak gallons per minute when the busy fixtures run together, the same fixture-unit thinking worked through in the water supply pipe sizing guide. The pump also has to make enough head to lift water from the pumping level and still hold system pressure at the top.

The hard rule is the one people break: do not size the pump past the well yield. A bigger pump on a weak well does not give you more water. It pulls the level down to the intake and sucks air, and you have spent money to pump the well dry faster. If the well gives 6 gpm and peak demand is 12, the answer is not a 12 gpm pump. It is a pump matched to the well plus a way to store water for the peak, either a large pressure tank or a separate storage tank with a booster.

For a low-yield well, the move is storage plus a right-sized pump, or a constant-pressure drive capped at the yield. Match the pump to the well first, then solve the demand peak with storage. Oversizing past the yield is the most expensive way to make a water problem worse, because now you own a pump that wears itself out chasing water the ground will not give.

Running the well dry and run-dry protection

Running dry is what kills a pump on a weak well. A pump that loses its water keeps spinning, and most well pumps rely on the water around them or moving through them for cooling and lubrication. Run a submersible dry and the motor overheats. Run a jet pump dry and it loses prime and burns its seals. Either way the pump dies from heat, not from wear.

The protection is layered. The first layer is sizing, covered above: a pump that cannot outrun the well cannot pump it dry. The second is a low-pressure cutoff or a dedicated low-water cutoff, which senses the loss of water, by pressure or by a probe set above the pump, and shuts the motor down before it cooks. The third, on a deep submersible, is a pump with built-in thermal or run-dry protection, more common on better units now.

On a well that goes dry seasonally, do not lean on the pump's own toughness. Add the cutoff and set it to protect the intake. The cheapest run-dry protection is far cheaper than a pump pull, and on a 300 ft well the pull is half the cost of the whole job before you have even bought the new pump.

The pitless adapter and the well head

The pitless adapter is the fitting that takes water out of the casing below the frost line. It is a two-piece connector: one half mounts through the casing wall underground, below frost, and the other half slides into it on the end of the drop pipe and seals with an O-ring. The horizontal water line runs out from there, underground, to the building. It replaced the old well pit, a buried vault around the wellhead that flooded and contaminated wells for decades, which is why pits are gone from modern code.

Above ground, the casing sticks up and gets a sanitary well cap. The cap seals the top of the casing against surface water, insects, and debris, with a screened vent so the well can breathe as the level moves. It should sit roughly a foot above grade, the exact height set by the health department or well code, so surface runoff cannot reach the casing top. The wellhead is the one part of the system open to the world, and the cap is what keeps the world out of your water.

Get the seal right or you get contamination. A loose cap, a cracked casing, or a flooded old pit lets surface water and bacteria straight into the aquifer you drink from. This is the part the health inspector looks at first on a well, before anything else, because it is where contamination gets in.

Check valves, foot valves, and keeping prime

A check valve keeps water from draining back down the well when the pump stops, which holds the system primed and saves the pump from refilling the whole drop pipe at every start. On a submersible there is usually a check valve at the pump and often a second one along the drop pipe on a deep set. Lose the check valve and water drains back, pressure bleeds off, and the pump cycles or runs long to refill, and a jet system loses prime entirely.

A foot valve is a check valve with a strainer built in, fitted at the bottom of the suction pipe on a jet pump. It does two jobs: it screens debris out of the intake, and it holds the water column in the suction pipe so the pump stays primed between runs. A jet pump that loses prime overnight and has to be re-primed every morning usually has a failed foot valve letting the column drain back down the well.

Priming is a jet-pump problem, not a submersible one. The submersible sits in the water and is always primed. The jet pump pulls from above and needs a full suction line and a wet pump body to grab water, which is why the foot valve matters so much on a jet, and one more reason a submersible is the lower-maintenance choice where depth allows it.

Freeze protection

Freeze protection on a well system comes down to keeping water below the frost line or inside heated space, and the pitless adapter is the reason the system can. The buried water line and the connection out of the casing both sit below frost, so the only water exposed to cold is inside the building. Set the depth of the line to the local frost depth with margin, because a line that freezes underground is a dig to fix.

The parts that freeze are the ones above ground in unheated space. A pressure tank and switch in an unheated well house, a pump house, or a vented crawl space will freeze and split if the heat fails, and a frozen switch or a burst tank takes the whole system down cold. Keep the tank and controls in conditioned space where you can, or heat and insulate the enclosure, and protect any exposed pipe.

For the deeper detail on frost depth, pipe burial, and protecting exposed runs, that is its own subject covered in the freeze and frost-protection material. The well-system part is short: below frost stays liquid, above grade in the cold does not, so the tank and switch belong somewhere warm.

The pump circuit and electrical

A well pump is a dedicated circuit, and on most submersibles it is 240 V single-phase. The pump gets its own breaker and a disconnect within sight of the controls, sized to the pump's nameplate, with GFCI or other protection per the adopted electrical code for the location and the equipment. Treat it as the motor circuit it is, with the overcurrent and disconnect rules that go with a motor.

The detail that trips well jobs is wire size over the depth. The cable runs from the surface down to a submersible 200 or 300 ft below, and that long run drops voltage, the same problem worked through in the voltage drop material. A pump fed by undersized wire over a deep set sees low voltage at the motor, draws more current, runs hot, and trips or fails early. The pump manufacturer publishes a wire-size chart by horsepower and total cable length for exactly this reason, and you size to that chart, not to the ampacity table alone.

Size the wire for the depth, use the manufacturer's chart, and confirm the circuit and protection against the adopted code. A deep pump on too-small wire is a slow failure that reads like a bad pump, and the replacement pump on the same wire fails the same way.

Water quality and treatment

Well water is untreated groundwater, and unlike city water nobody disinfects or conditions it before it reaches the tap. What comes up depends on the geology, and common issues are hardness, iron and manganese that stain, sulfur smell, low pH that eats copper, and bacteria or nitrates that make the water unsafe. Test the water before you assume it is fine, and test it on a schedule after.

Treatment is matched to the test, and it is its own trade covered in the water-treatment material, but the well-system point is that treatment lives downstream of the pressure tank, not in the well. A softener, a neutralizer, an iron filter, or a UV sterilizer goes on the line after the tank, sized to the system flow. Put treatment ahead of the tank and you fight the pump and the pressure, so the order is well, pump, tank, then treatment.

The baseline test most health departments want is coliform bacteria and nitrate, plus whatever the local geology is known for. Do not guess at treatment. A water test tells you what you have, and the equipment follows the test, not a sales pitch.

No water or low pressure: where to look

When a well system loses pressure or quits, work it from cheap and easy toward deep and expensive, because the deep fixes cost the most and the cheap faults are more common. Start at the panel: a tripped breaker or a blown fuse is the first check, and a breaker that trips again right after reset points at the pump or the wiring, not the breaker.

Then the controls and tank. Check the pressure switch, its contacts and its sensing port, which clogs. Check the tank pre-charge and whether it is waterlogged, the short-cycling check from earlier. A dead switch or a dead tank fakes a lot of pump symptoms. If the pump runs but pressure is low, look at a clogged filter or treatment unit, a partly closed valve, or a pump losing output. If the pump runs and runs and never builds pressure, suspect a lost check valve, a leak in the drop pipe, or a well drawn down below the pump.

If the pump will not run at all and the breaker is good, it is the switch, the control box on a 3-wire, the wiring, or the pump itself, in that order of cost. Confirm power is reaching the switch and leaving it before anyone pulls a pump. Pulling a good pump on a bad switch is the expensive mistake on these calls.

Maintenance and what to check

A well system asks for little, but the little it asks for prevents the big failures. Once a year, check the tank pre-charge with the system drained and the pump off, and reset it to about 2 psi below cut-in if it has drifted. A tank slowly loses air, and catching it before it goes waterlogged saves the pump. While you are there, watch a full pump cycle and time it: a pump that runs and rests in cycles of a minute or more is healthy, one cycling every few seconds is telling you something is wrong.

Test the water on a schedule, at least yearly for bacteria and nitrate and after any work that opens the system. Look at the wellhead: cap tight, casing sound, ground sloped away so runoff drains off rather than in. Check the pressure switch contacts if the pump is slow to start or chatters.

The pump itself is the part you do not service, you replace. A submersible commonly lasts 10 to 15 years, longer on a system sized right and not cycling, far shorter on one that short-cycles or runs dry. The maintenance that matters is not on the pump. It is on the tank, the switch, and the wellhead, the cheap parts that protect the expensive one.

Shock chlorination and well sanitation

Shock chlorination is how you disinfect a well after a positive bacteria test, after pump work that opened the system, or after flooding reaches the wellhead. You introduce a strong chlorine solution into the well, circulate it through the casing and the whole plumbing system until you smell chlorine at every tap, let it sit for the contact time the procedure calls for, commonly several hours to overnight, then flush it all out and retest after the chlorine clears.

It is a treatment for an event, not a cure for a source. If a well keeps testing positive after a proper shock, the contamination is getting back in, which means the wellhead seal, a cracked casing, a flooded pit, or surface water has a path. Fix the entry point or you will be shocking the well forever. Chlorine kills what is in there now. It does nothing about the hole that let it in.

Follow the health department's procedure for dose and contact time, because the amount of chlorine depends on the well's depth, diameter, and water volume, and retest before you call the water safe. Do not drink the water until the retest is clean, and run the chlorinated water out onto the ground, not into a septic system in a slug that can upset it.

Larger private supplies and booster systems

The same parts scale up to larger private supplies, a small water system for a campus, a farm, a development, or a data center, and the logic does not change so much as multiply. The well or wells feed storage, and a booster pump system takes water from storage and holds pressure for the building, often with several pumps and a VFD on a constant-pressure setup. The pressure tank becomes a smaller buffer because the booster and drive carry the pressure.

The reason to split the well pump from a booster on a bigger system is that the well pump should run at the well's sustainable yield to fill storage, while the booster sizes to the building's peak demand, which can be far higher than the yield for short bursts. Storage absorbs the gap. The well fills the tank slowly and steadily, the booster pulls fast when the building calls, and neither one is asked to do the other's job.

On a critical supply like a data center, the design carries redundancy the house well does not: duplicate pumps, duplicate boosters, generator-backed power, and stored volume to ride through a well or power problem. The single-pump, single-tank house system is the same idea stripped to its minimum, and everything bigger is that minimum with redundancy and storage added.

What to document

The well system is half buried and out of sight, so the record is how the next person knows what is down the hole without pulling it. Capture it at install and update it at every service. The driller's well log is the foundation: depth, casing, static level, and tested yield. The pump, tank, and switch data make up the rest.

Without a record, the next service call starts by guessing the pump depth, the wire size, and the switch settings, and guessing on a well is slow and expensive.

Common mistakes

• Letting a waterlogged tank short-cycle the pump until the motor burns out instead of fixing the tank.
• Setting the air pre-charge to a guess instead of about 2 psi below the switch cut-in, or checking it with the tank full of water.
• Sizing the pump past the well yield, which pumps the well dry instead of delivering more water.
• Running a weak well with no low-pressure or run-dry cutoff, so the pump cooks when the well draws down.
• Putting a shallow-well jet on a well deeper than its suction limit and wondering why it will not lift water.
• Losing a check valve or foot valve and the prime that goes with it, then chasing it as a pump problem.
• Feeding a deep submersible with undersized wire, so voltage drop over the depth burns the motor.
• Changing the switch settings and forgetting to reset the tank pre-charge to match.

Field checklist

Standards and references

Well systems are governed by more than one authority, and they do not all live in the plumbing code. The pump and pressure tank carry the manufacturer's installation data: the wire-size charts, the pre-charge specs, and the pressure ratings, and that data controls the equipment-specific numbers. The plumbing code, the IPC or UPC as adopted, governs the water distribution inside the building from the tank onward.

The well itself is usually a state and county health-department matter, not the plumbing code. Well permits, the minimum setbacks from septic systems and property lines, casing and grouting requirements, the wellhead height, and the disinfection procedure come from the health department and the state well code, and they vary by jurisdiction more than almost anything else in plumbing. The National Ground Water Association, the NGWA, publishes standards and guidance the trade leans on. The electrical side follows the adopted electrical code, the NEC where it is in force, for the pump circuit, the disconnect, and the protection.

Hedge every number to its source. The pressure settings and pre-charge follow the tank and switch manufacturer. The setbacks and well construction follow the health department and the adopted well code. The wire size follows the pump manufacturer's chart and the electrical code. Confirm the adopted editions and any local amendments before you cite any of it on a permit, because well rules in particular are local.

Units and terms

Well-system numbers come in a few units and a lot of trade names for the same thing, so a spec sheet, a driller's log, and a pump curve can describe one system three ways.

Flow is gallons per minute, gpm, sometimes gallons per hour on small pumps. Pressure is psi at the tank and switch, and the same pressure shows up as feet of head on a pump curve, where about 2.31 ft of head equals 1 psi. Depth and water levels are in feet. Pump capacity is rated as gpm at a given head, so a pump is not just so many gpm, it is so many gpm against the head it has to work.

Static water level

Where water stands in the casing with the pump off

Pumping level / drawdown level

Where water falls to while the pump runs

Drawdown

The drop from static to pumping level; also the gallons a tank delivers between cut-out and cut-in

Yield

The gpm the well sustains over time, the ceiling on pump sizing

Cut-in / cut-out

The pressures where the switch starts and stops the pump, for example 30/50 psi

Pre-charge

The tank air pressure, set about 2 psi below cut-in with the tank empty

Head

Pressure expressed as feet of water; about 2.31 ft equals 1 psi

Specific capacity

Well yield per foot of drawdown, for example 1 gpm per foot

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