Water well drilling and private well systems field guide

A water well, and the seal that matters as much as the water

A private water well is a cased hole drilled down to an aquifer, with a pump that lifts groundwater out of the ground and pushes it into the building. That is the part everyone pictures. The part that decides whether the water is safe to drink is the sanitary seal: the casing grouted into the ground so surface water, septic effluent, and contamination cannot run down the outside of the pipe and into the aquifer you are pulling from.

Think of it as two jobs that happen to share a hole. One job is hydraulic, getting enough water out at enough pressure. The other is sanitary, keeping the bad water out of the good. The hydraulic job gets all the attention because it is the one a homeowner notices when a tap runs slow. The sanitary job is the one that poisons a family quietly when it is done wrong, because contaminated water from a well often looks and tastes fine.

The work, start to finish, is a short list done in order. Site the well away from contamination sources. Drill and case it. Grout the annulus from the surface down so there is no path along the outside of the casing. Size the pump to the well's depth and yield. Set the pitless adapter below the frost line. Test the water and disinfect the well before anyone drinks from it. Every one of those steps answers to the state well-construction code and the health department, and most of them are reserved for a licensed driller and pump installer. The pump, pressure tank, and switch that run the house are their own subject, covered in the well pump and pressure tank guide; treating the water once it is in the building is covered in the water treatment guide.

How does a water well work?

A water well works by reaching a water-bearing layer underground, holding the hole open with casing, and pumping the groundwater up to the surface. Below your feet, water fills the pore spaces and fractures in soil and rock. The depth at which those spaces are fully saturated is the water table, and a layer that holds and yields usable water is the aquifer. The well is simply a controlled opening into that saturated zone.

When the pump is off, water in the casing rises to the static water level, which is the natural pressure level of the aquifer at that spot. Start pumping and the level in the well drops. That drop is drawdown, and it stabilizes at a pumping level where the water flowing in from the aquifer matches what the pump is taking out. The rate the well can sustain at that balance, measured in gallons per minute, is the yield.

Those three numbers, the static level, the drawdown, and the yield, describe the well as a water source and they set everything downstream. They tell you how deep the pump has to hang, how hard it has to work to lift the water, and whether the well can keep up with the house. Get them measured before you size anything, because guessing here is how pumps end up hanging in the wrong place pumping a well dry.

How is a well sealed from contamination?

A well is sealed from contamination by the casing and the grout around it, together called the sanitary seal, and it is the single most important thing a well driller builds. The casing is the pipe that lines the hole. The grout is the sealing material packed into the annular space, the gap between the outside of the casing and the wall of the borehole. Grouted from the surface down, it closes off the one path contamination takes most easily: straight down the outside of the casing.

That path is the problem the seal exists to solve. Rain, irrigation runoff, snowmelt, a flooded yard, a leaking septic field, spilled chemicals, manure: all of it carries bacteria, nitrate, and worse, and all of it wants to follow the casing down into the aquifer. An ungrouted or poorly grouted annulus is an open channel for it. A well can sit a safe distance from every contamination source and still be unsafe if the annular seal lets surface water shortcut down the pipe.

This is the one detail to get right above all the others, and it is the one a homeowner can never inspect after the fact, because it is buried the day it goes in. The required grout material, the depth it must extend, and how it is placed are all set by the state well code and the health department, and they vary by jurisdiction and by geology. Treat the seal as the part of the job you do not cut corners on, and let the licensed driller and the code govern the specifics.

Drilling methods: rotary, cable tool, and air

Most modern water wells are drilled one of a few ways, and which one fits is decided by the geology under the lot, not by preference. The rock and soil sequence is what drives the method, and a driller who works an area knows the local formations cold.

Mud rotary spins a bit while drilling fluid is pumped down the drill pipe to flush cuttings up and out. The fluid also holds the borehole wall open, which is why mud rotary is the common choice in unconsolidated ground like sand, gravel, and clay, where an open hole would cave. There is essentially no practical depth limit. Air rotary uses compressed air instead of mud to clear the cuttings, often with a down-the-hole hammer, and it is fast in hard rock like granite and fractured bedrock. Cable-tool, or percussion, is the old method: a heavy bit is raised and dropped on a cable to pound the hole down. It is slow, but it needs no mud or air, it gives a clear picture of the formation as it goes, and it still earns its place in certain ground.

Each method has tradeoffs in speed, cost, and how cleanly it leaves the water-bearing zone, and mud rotary in particular requires careful development afterward to clear the drilling fluid out of the aquifer. The right method for a given site, and whether a method is even allowed in a given aquifer, is a call for the licensed driller working to the state code.

The casing

The casing is the pipe that lines the drilled hole. It keeps the borehole from collapsing, holds back loose formation, and seals off the shallow, often contaminated zones near the surface so the well only draws from the deeper water you want. It is the structural and sanitary spine of the well, and it is what the grout seals against.

Casing is commonly steel or PVC. Steel is strong and takes the punishment of driving and deep settings, but it corrodes over time, especially in aggressive water, and a corroded casing can open holes that let shallow water in. PVC does not corrode, is lighter and cheaper, and is common in many domestic wells, but it has a depth and collapse-pressure limit that the manufacturer specifies, and it has to be handled so the joints stay watertight. The choice depends on depth, water chemistry, and what the code allows.

Two casing dimensions matter on every job. The diameter has to fit the pump and leave clearance, so a 4 inch casing that will not pass a larger pump is a problem you discover at the worst time. The depth, and specifically how far the casing extends below the surface and how far above grade it stands, is set by code, often a minimum of about 12 inches above finished grade, but confirm the required casing depth, diameter, material, and stickup against the state well code and the health department.

The grout seal

Grout is the sealing material placed in the annular space around the casing, and grouting that space from the surface down is what turns a lined hole into a sanitary well. Without it, the gap between the casing and the borehole wall is an open conduit for surface water. With it, that conduit is filled and the only way into the aquifer is up through the screen at the bottom, the way you intended.

The two common grout materials are neat cement, which is cement and water with no sand, and bentonite, a clay that swells when it hydrates and presses tight against the casing. Each has its place depending on depth, formation, and code, and each has to be placed correctly, usually pumped from the bottom of the annulus up so it fills the space without bridging and leaving voids. A grout job that bridges and leaves an air gap partway down has failed even if the top looks finished.

How deep the grout must extend, which material is required, and how it must be placed are not driller's-choice details. They are spelled out in the state well-construction code and enforced by the health department, and the requirement can be the entire annulus or a specified minimum depth from the surface depending on jurisdiction and geology. This is the place to follow the code to the letter, because it is the protection that cannot be added back later without pulling the well apart.

The screen and open hole

At the bottom, the well has to let water in while keeping sand and grit out. In hard rock, that is often just open hole below the casing, where the fractured rock yields water and stands on its own. In unconsolidated formations like sand and gravel, it takes a well screen: a slotted or perforated section of pipe sized to admit water and hold back the formation.

The slot size is the key number on a screen. Too wide and the well pumps sand, which wears the pump and fills the bottom of the well. Too narrow and the screen clogs and chokes the yield. In a naturally developed well the slot is sized to retain most of the surrounding formation. In a gravel-packed well, a graded filter sand or fine gravel is placed in the annulus around the screen, and the slot is sized to retain the pack rather than the formation, which lets you run a more open slot for better flow.

Screen length, slot size, and whether a gravel pack is warranted are engineered to the aquifer's grain size, and getting them right is what separates a sand-free well from a pump-killer. This is design work for the driller based on the formation samples from the borehole, governed by the state code and good practice.

Well development

A freshly drilled well is not finished when the hole is done. The drilling leaves fine material, drilling mud, and disturbed formation in and around the screen, and that has to come out before the well will give clean water at its full yield. Pulling those fines out is well development.

Development is done by moving water back and forth through the screen and the formation, surging it, then pumping the loosened fines out, repeated until the water runs clear and the yield holds steady. Surge blocks, air, or just hard pumping cycles are used depending on the well. The aim is two things at once: clear the water and build a stable, graded zone in the formation around the screen that keeps fine sand from migrating in later.

Skip development or quit early and the well pays for it forever, pumping sand, plugging the screen, and never delivering the yield the aquifer could give. A well that pumps sand from day one was usually under-developed, not badly drilled. The driller decides when development is complete by clarity and sustained yield, not by the clock.

The aquifer and static water level

The aquifer is what you are tapping, and it is worth understanding as more than a hole full of water. It is a formation, sand, gravel, sandstone, or fractured rock, that holds water in its pores and fractures and is permeable enough to give it up to a well. Some aquifers are shallow and quick to recharge from rain. Some are deep, confined under a layer that holds them under pressure, and recharge slowly over years.

The static water level is the depth to water with the pump off, and it reflects the aquifer's pressure at that location. It is not fixed. It moves with the seasons, falls in drought, and drops when neighboring wells pump hard from the same aquifer. A well drilled in a wet spring against a shallow static level can come up short by late summer when the level falls, which is why the static level alone is not the whole story.

What the aquifer is, how deep it sits, how it recharges, and how reliable it is over a dry year are questions for local hydrogeology and the driller's experience in the area, not something to assume from a single measurement. The depth, water quality, and yield of a given aquifer vary widely by region, so lean on the licensed driller and local records.

What is well yield, and how is it tested?

Well yield is the rate, in gallons per minute, that a well can sustainably deliver, and it is measured with a well test, not estimated. The test pumps the well at a steady rate, measures how far the water level draws down and holds, and then measures how fast the level recovers after the pump stops. Those numbers together tell you whether the well can supply the home.

Drawdown and recovery are the heart of it. A well that drops only a little under steady pumping and recovers fast has plenty of capacity. A well that draws down deeply and recovers slowly is near its limit, and pumping it harder than its recovery rate just pulls the level down to the pump and runs it dry. Specific capacity, the yield divided by the drawdown, is the cleaner measure of well performance and a useful baseline to compare against years later when you suspect the well is declining.

For a typical house, many in the trade treat roughly 5 gpm as the lower end of an adequate well and call something in the 8 to 12 gpm range comfortable, but those are rules of thumb, not a code threshold. A low-yield well can still serve a home with storage and the right pumping strategy. Whether a given well can supply a particular household depends on the household's peak demand, the available storage, and the local code's well-test and yield requirements, so size to the tested yield and confirm against the state code and the health department.

The submersible pump and total dynamic head

The submersible pump is the workhorse of a drilled well. It is a sealed motor-and-pump unit that hangs down in the water and pushes water up the drop pipe, rather than sucking it from the surface, which is why it handles deep wells a jet pump cannot. Sizing it comes down to two questions: how much water (gpm) the house needs, and how hard the pump has to work to deliver it, which is the total dynamic head.

Total dynamic head, or TDH, is the sum of everything the pump fights against. It is the depth from the pumping water level up to the surface, plus any rise from the wellhead to the house and tank, plus the pressure you want at the tank converted to feet, roughly 2.31 feet of head per psi, plus the friction loss in the drop pipe and the line to the house. Add those up and you have the head the pump must overcome at the flow you need. You then pick a pump and horsepower off the manufacturer's pump curve that meets that gpm at that TDH.

The two failures here are mirror images. An undersized pump cannot make pressure or keep up with demand. An oversized pump pulls the well down faster than it recovers, breaks suction, and burns up running dry, and it short-cycles the pressure tank. Match the pump to the well's tested yield first, then to the head and flow the house needs. The pump, tank, and switch as a working system are covered in the well pump and pressure tank guide; size to the manufacturer's curve and the data for the specific pump.

The drop pipe, wire, torque arrestor, and safety rope

The drop pipe is what the pump hangs on, and it carries the water up. It is sized for the flow so friction loss stays reasonable: a 1 inch drop pipe is common up to roughly 10 gpm, and stepping up to 1.25 inch cuts the friction loss sharply at higher flows. Run too small a drop pipe at high flow and you add head the pump has to fight for no reason. The setting depth, how far down the pump hangs, is chosen to keep the pump submerged below the pumping water level with margin, while staying above the screen so it does not pull sand.

The submersible wire runs down alongside the drop pipe to power the motor, and it is sized for the motor's amps and the run length, because voltage drop over a few hundred feet of small wire starves the motor the same way it starves any load. A torque arrestor is fitted near the pump to absorb the twisting jolt each time the motor starts, which otherwise lets the pump swing and rub against the casing and chafe the wire. A safety rope, secured at the top, holds the pump if the drop pipe ever fails, so a dropped pump can be retrieved instead of fished from the bottom.

These are the install details that decide whether the pump lasts twenty years or fails early, and they are pump-installer work. Follow the manufacturer's instructions for wire size, splice method, torque arrestor placement, and setting depth, and the state code for who may do the work.

What is a pitless adapter?

A pitless adapter is the fitting that takes the water out of the well casing horizontally, below the frost line, so the line to the house never freezes and there is no pit to build. It replaced the old well pit, an underground room around the wellhead that flooded, harbored vermin, and was itself a contamination route. The pitless adapter does the same job, getting the water sideways and underground, without any of that risk.

It is a two-part fitting. One half is bolted permanently through a hole in the side of the casing, sealed watertight to the casing wall, with the buried service line to the house connected to it. The other half is attached to the top of the drop pipe and slides down into the casing-mounted half, sealing against it so water turns and flows out horizontally through the casing wall. Because the pump hangs from that sliding half, you can pull the whole pump and drop pipe straight up for service without digging, while the casing-side connection stays put.

The one rule that cannot be missed: the adapter, and the buried line running from it to the house, must sit below the local frost line, which can be several feet down in cold climates. Set it shallow and the horizontal run freezes solid in the first hard winter. The required burial depth is set by the local frost depth and the code, so confirm the frost line for the jurisdiction before you cut the casing.

The sanitary well cap

The well cap seals the top of the casing, and it is the part of the sanitary seal you can actually see. A proper sanitary cap keeps surface water, insects, rodents, and debris out of the top of the well, and it is vented so the water level can rise and fall without pulling a vacuum. The vent is screened and turned down so nothing crawls in through it.

The casing has to stand above grade for the cap to do its job, commonly a minimum of about 12 inches above finished grade, so surface water and flooding cannot reach the opening. A casing cut off at or below grade is a contamination route waiting for the next heavy rain, and it is one of the more common defects an inspector flags on an older well. The cap should be the vermin-proof, gasketed type secured with screws, not a loose slip cap.

The above-grade height, the cap type, and the vent details are specified by the state code and the health department. Where a cap is damaged, missing, or sitting on a casing cut too low, that is a finding to correct, because the best grout job in the world does not help if the top of the well is open.

The pressure tank, switch, and house system

Once the water is up and into the building, the pressure tank and switch take over. The tank stores a few gallons under air pressure so the pump does not have to start every time a tap opens, and the pressure switch cycles the pump between a cut-in and cut-out pressure, commonly 30/50 or 40/60 psi. A constant-pressure system using a variable-speed drive is the alternative when steady pressure matters.

That whole system, the tank sizing, the air pre-charge, the switch settings, and the short-cycling and run-dry failures that kill pumps, is its own subject. It is covered in detail in the well pump and pressure tank guide, and the short version is that most well-system callbacks are the tank or switch driving the pump into a failure, not the pump dying on its own.

What matters for the well itself is that the pump you sized for the well's depth and yield has to match the pressure system it feeds. Size them as one system, not three parts bought separately.

How often should well water be tested?

Private well water should be tested at least once a year for total coliform bacteria and nitrate, with broader chemical testing every few years, because a private well is not treated or monitored by anyone but the owner. There is no utility checking it. The water can carry bacteria, nitrate, arsenic, or other contaminants and look, smell, and taste completely normal, which is exactly why testing is the only way to know.

The two annual tests carry the most weight. Total coliform and E. coli flag a contamination pathway into the well, often a failing seal or a nearby source, and the standard for safe drinking water is zero coliform. Nitrate above 10 mg/L is a real hazard, especially for bottle-fed infants under six months, where it causes methemoglobinemia, the blue-baby condition. Beyond those, test for whatever the local geology and land use put at risk: arsenic, manganese, hardness, iron, and any contaminant flagged in the area.

Test more often, and right away, after any change: flooding, new construction or land disturbance nearby, a known contamination event, or any work on the well. The specific tests, action levels, and recommended schedule come from the EPA private-well guidance, the CDC, and your state or county health department, so follow their list for your area. If a test comes back with a treatable problem like hardness, iron, or low pH, fixing it is covered in the water treatment guide, but treatment never substitutes for finding and closing the contamination path.

Disinfecting the well after drilling or repair

Any time a well is drilled, opened, or worked on, it gets disinfected before the water is used for drinking, because the tools, pipe, and pump that go down the hole carry surface bacteria with them. Shock chlorination is the standard method: a strong chlorine solution is introduced into the well, circulated through the casing and the whole plumbing system, held, then flushed out.

The procedure matters in the details. The well is dosed with chlorine, commonly using unscented household bleach at a rate worked out for the volume of water in the casing, then the solution is pulled through every fixture by running each tap until the chlorine smell shows, so the entire system is treated and not just the well. It is held for several hours, often 12 to 24, then flushed until the chlorine is gone, with care not to dump the heavy chlorinated water where it will damage a septic system or landscaping.

After flushing, you wait several days and then retest for coliform to confirm the disinfection actually worked, because shock chlorination kills what is there but does not fix an ongoing source. A well that keeps coming back positive after a proper shock has a problem upstream, usually a seal or a setback issue, that chlorine cannot solve. The exact dose, contact time, and procedure should follow the health department guidance for your area and the equipment manufacturer's instructions.

How far should a well be from a septic system?

A well has to sit a code-required minimum distance from any septic system and other contamination sources, and the most commonly cited figure is 100 feet from a septic leach field, though it ranges and is set locally. The point of the setback is to put soil and distance between the contamination source and the well, so anything leaching into the ground is filtered and diluted before it can reach the aquifer the well draws from.

Septic is the usual concern, but it is not the only one. Setbacks also apply to the septic tank itself, sewer lines, livestock yards and manure, fuel tanks, chemical storage, property lines, and surface water. Each has its own required distance, and the numbers vary by state and county and by the type of source. There is no single federal number; the county health department sets the enforceable rules for the area, and they can be tighter where the soil is fast-draining or the aquifer is shallow and vulnerable.

Siting is the cheapest contamination control there is, because it costs nothing to put the well in the right place before drilling and a fortune to fix a well drilled too close. Setbacks work together with the grout seal: distance keeps the source away, and the seal keeps surface water from shortcutting down the casing regardless. Confirm every required setback against the state well code and the local health department before the rig is positioned, not after.

Treatment and freeze protection

Well water comes up untreated, exactly as the aquifer holds it, so if the test finds hardness, iron, manganese, low pH, or a contaminant, the water gets conditioned at the building. A softener handles hardness, oxidizing filters and air injection handle iron and manganese, a neutralizer raises low pH, and reverse osmosis or UV handle dissolved solids and bacteria. Matching the right device to the test result, in the right order and sized to the flow, is the whole of that work and it is covered in the water treatment guide. Treat the problem the test actually found, not the one the brochure sells.

Freeze protection on a well comes down to keeping water out of the cold. The pitless adapter and the buried service line do the heavy lifting by carrying the water below the frost line, which is why a properly set pitless is the freeze defense for the well itself. Above grade, the pressure tank, switch, and any treatment equipment live inside a heated space or a well house kept above freezing, because they are full of water at low flow and freeze fast in an unheated corner.

The failure to watch for in cold climates is a pitless or service line set too shallow, which turns the one reliably warm part of the system into the part that freezes. Set the buried work below the local frost line and keep the indoor equipment warm, and the system rides out winter.

Do I need a permit and a licensed driller?

In nearly every jurisdiction a private well requires a permit and must be drilled by a licensed well driller, and the pump is installed by a licensed pump installer, with a well log filed afterward. This is not paperwork for its own sake. The licensing and the permit are how the state enforces the construction standards, the casing, the grout seal, the setbacks, that protect the aquifer and everyone who drinks from it.

The well log, sometimes called the well completion report or well record, is the well's birth certificate. It records the depth, the casing material and depth, the grout, the static water level, the yield from the well test, the formation log, and the pump installed. It is filed with the state and it is the document that tells the next owner, the next pump installer, and the health department what is actually in the ground. A well with no log is a well nobody can troubleshoot without guessing.

Permitting requirements, who may legally drill and install, the well-test standards, and the filing deadlines all live in the state well-construction code and are administered by the health department or the state water agency. They vary by state, so confirm the permit, the licensing requirement, and the reporting before any work starts. Drilling a well without a permit or a licensed driller is not a shortcut; it is how a well gets ordered abandoned and a property loses its water supply.

What to document

The well log filed with the state is the official record, but a contractor keeps a parallel set for the work, because the day a well goes bad the questions all come back to what was built and tested. A field tool like FieldOS keeps the well-test numbers, the construction details, the water results, and the photos in one place tied to the property, so the next service call starts from facts instead of a homeowner's memory.

Capture the construction, the performance, and the water. The construction is the depth, casing material, diameter and depth, screen, and grout. The performance is the static level, the drawdown, the tested yield, and the pump model, horsepower, and setting depth. The water is the test results and the disinfection. Record who did the work and the permit and well-log numbers, because that ties the whole record back to the official filing.

Common mistakes

• No grout seal, or a grout job that bridged and left voids, letting surface water run down the casing into the aquifer.
• Well sited too close to a septic system, livestock, fuel, or chemical storage instead of the code setback.
• Pump oversized for the well's yield, pulling it down faster than it recovers and running dry, or undersized and unable to make pressure.
• No water-quality test, so contamination that looks and tastes normal goes undetected.
• No disinfection after drilling or a pump repair, leaving the bacteria the work introduced in the well.
• Pitless adapter or buried service line set above the frost line, so the horizontal run freezes in winter.
• Casing cut off at or below grade with no proper sanitary cap, leaving the top of the well open to surface water.
• No permit, no licensed driller, and no well log, so there is no record and no enforced standard behind the well.

Field checklist

Standards and references

The governing document for a private well is the state well-construction code, administered by the state health department or water agency, with the county health department often setting and enforcing the local setbacks and permits. The casing material and depth, the grout type and depth, the required setbacks, the well-test standard, and who may legally drill and install are all set there, and they vary by jurisdiction and by geology. Confirm every one of them against the adopted code for the location before relying on a number in this guide.

The licensed well driller and pump installer carry the construction standards in practice, and the manufacturer's data governs the pump, the pitless adapter, the casing, and the treatment equipment, including the pump curve, wire sizing, setting depth, and pressure ratings. The EPA private-well guidance and the CDC set the recommended water-testing schedule and the drinking-water limits, including zero coliform and the 10 mg/L nitrate MCL, while the health department defines the local action levels and the disinfection procedure.

Three things carry this work: the grout seal and the setbacks protect the drinking water, the pump is sized to the depth and yield with the pitless set below frost, and the water is tested and disinfected to the state well code. Where this guide gives a figure, treat it as a common practice to verify, not a code mandate, and let the state code, the licensed driller, and the health department control.

Units and terms

Well work mixes hydrogeology, plumbing, and electrical terms, so the same well gets described in a few different vocabularies across a driller's log, a pump submittal, and a health department report.

Yield is in gallons per minute (gpm). Depths and water levels are in feet. Pressure is in psi, and head is in feet, related by roughly 2.31 feet of head per psi. Nitrate limits are in mg/L. The terms below are the ones that carry the most weight on a private well.

Water well

A cased hole drilled to an aquifer, with a pump that lifts groundwater to the building

Aquifer / static water level

The water-bearing formation, and the depth to water in the well with the pump off

Casing and grout (sanitary seal)

The pipe lining the hole plus the grout sealing the annulus, which stops surface contamination from running down into the aquifer

Well screen

The slotted intake in the aquifer that admits water and holds back sand, sized by slot to the formation or gravel pack

Drawdown / yield

How far the water level falls under pumping, and the sustainable rate in gpm the well delivers

Submersible pump

A sealed motor-and-pump unit set down in the water that pushes water up the drop pipe, sized to gpm and total dynamic head

Pitless adapter

The fitting that takes water out of the casing horizontally below the frost line, replacing the old well pit

Well disinfection

Shock chlorination of the well and plumbing after drilling or repair, followed by a confirming retest

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