The mistake at the centre of every well conversation
Someone runs a hose for ten minutes, fills a bucket, times it, gets ten gallons a minute and reports that they have a ten gallon a minute well. They do not. They have measured the pump.
A drilled well is a vertical tank with a hole in the side. The casing holds water — a six inch casing holds about 1.47 gallons for every foot of standing water, so a well with 160 feet of water in it is storing well over two hundred gallons before the formation contributes anything at all. Pump hard for ten minutes and most of what comes out is that stored water. The formation, which is the actual well, may have been trickling in at a fraction of a gallon a minute the whole time.
The consequence is not academic. A house plumbed on the strength of a short test works beautifully in April and runs the pump dry in August with three guests staying, and the owner concludes the pump has failed. It has not. The well was always this well.
What each measurement tells you
| Measurement | What it describes | What it does not |
|---|---|---|
| Pumping rate | The pump and the plumbing | Anything whatsoever about the aquifer |
| Static water level | The pressure head in the formation, on that day | How much water there is, or how fast it moves |
| Drawdown during a short test | Mostly how much casing storage you consumed | The sustainable rate |
| Drawdown that stabilises over a long test | The rate at which the formation feeds at that head — a real yield figure | Behaviour in a drought, or after the neighbour drills |
| Recovery rate | How fast the formation refills the hole — the closest thing to a yield a homeowner can measure | Long-term aquifer capacity |
Recovery is the honest measurement because during recovery the pump is not involved. Water is entering the casing from the formation and nothing else is happening. If the level rises 30 feet in an hour in a six inch casing, that is 30 × 1.47, or about 44 gallons in sixty minutes, which is 0.73 gallons a minute. Whatever the pump did, that is what the ground gives.
One caveat that keeps the figure honest: recovery is fastest at the start, when the head difference between the aquifer and the low water in the casing is greatest, and it slows as the level approaches static. A recovery rate measured over the first hour therefore reads slightly high compared with the long-run average. It is still enormously closer to the truth than the pump rate.
Doing the test properly
The version worth doing is not complicated, but each step matters.
- Rest the well for several hours with nothing drawing, and measure the static level. A tape with a chalked end, or an electric sounder, read at the well head.
- Pump at a steady, known rate. Known means timed into a container of known volume, not assumed. Discharge well away from the well.
- Pump for far longer than feels necessary. Ten minutes tests the casing. Several hours starts to test the aquifer. A well test performed for a mortgage or a sale usually runs for hours for exactly this reason.
- Measure the level at intervals throughout, not only at the end. What you want to see is whether it falls and then stabilises — a stable level under continuous pumping is a genuine yield figure at that rate.
- Stop, and measure recovery at intervals. Time and level, several readings, until it is close to static.
If any of that is beyond what you can do at the well head, a licensed well contractor does it as routine work, and the report they produce is the document that a lender, a buyer or a health department will actually accept.
Living with a low yield well
Plenty of houses run on wells producing under a gallon a minute, and they run fine, because the fix is storage rather than a bigger pump. A slow well filling a cistern around the clock accumulates a large volume, and the house draws fast from the cistern through a booster pump. A well producing 0.7 GPM continuously delivers about a thousand gallons a day, which is more than most households use — the problem was never the daily total, it was the instantaneous rate. That is exactly what the cistern sizing calculator is for.
The other half of the answer is protecting the pump. A pump that runs dry burns out, and the standard protections are a low water cut-off, a flow or pressure sensing control, or a timer that limits run time. Which is appropriate is a question for the well contractor, and the pressure side of the system — cycling, run times, tank drawdown — belongs on the pressure tank calculator. If the pressure at the well is fine and at the far fixtures it is not, the loss is in the pipe and the pressure drop calculator will find it.
What this page does not touch
Nothing here says anything about whether the water is fit to drink, and it should not. A private well is not tested by anyone unless the owner arranges it, and what to test for, how often, and what to do about a result are questions for your local or state health department and an accredited laboratory. Treatment selection follows the lab report, not a web page.
It also says nothing about well construction, casing depth, grouting, setbacks, abandonment of an old well, or whether a well may be drilled where you want one. Those are licensed and permitted matters everywhere, they interact directly with septic system placement on the same property, and they are settled with the well contractor and the health department. Wells and drainfields on one lot are two halves of the same site plan, and neither can be positioned without the other: the drainfield organizer is the other half of that conversation. Before any digging near a tank, a field or a supply line, call the national dig line and have the utilities located. Free, required in practice everywhere, and it takes days rather than minutes, so make the call before you rent anything. Once a drainfield is in the ground, keep vehicles, trailers, livestock and stored material off it. The gravel and the soil structure under it are what make it work, and compaction from a single truck parked on a wet field can end its life.
Questions people ask
How do I know what my well yield actually is?
Measure the recovery, not the flow. Rest the well, record the static level, pump at a known steady rate for as long as you can manage, record the level when you stop, then record it again after a measured rest. The rise in feet multiplied by the gallons per foot of your casing, divided by the minutes, is a recovery rate in gallons per minute, and that number behaves like a yield in a way that the pump rate never does. A six inch casing is about 1.47 gallons per foot; a four inch is about 0.65. If the well is being bought, sold, or newly equipped, have a licensed well contractor run a proper multi-hour test — the difference between their test and a homeowner one is duration and instrumentation, and it matters.
My well runs out after twenty minutes of watering. Is the pump failing?
Probably not. That symptom is the signature of a well whose recovery rate is well below what you are drawing, so you are running on stored casing water and then hitting the bottom of it. Work out the storage above the pump intake, work out the recovery rate, and the arithmetic usually explains the twenty minutes exactly. The fixes are storage, a lower draw rate, or both, and the thing to check first is that the pump has some form of dry run protection, because repeatedly pulling a submersible into air is how they die. A well contractor is the person to confirm the diagnosis and fit the protection.
Does a bigger pump get more water out of a low yield well?
No, and it makes the situation worse. The formation feeds at the rate the formation feeds at. A larger pump only empties the casing faster, so you reach the point of running dry sooner, and you have added a motor that is even less tolerant of doing so. The only things that increase what a well delivers over a day are storage between the well and the house, reduced or spread-out demand, and physical work on the well itself — deepening, hydrofracturing or cleaning — which is well contractor territory with no guarantee of a result.
Why is my static level different from last year?
Static levels move, and several unrelated things move them. Season is the largest for most wells, with levels typically lowest at the end of a dry period and highest after recharge. Multi-year drought shifts the whole baseline. New pumping nearby, whether a neighbour's well, irrigation or something industrial, can draw the level down across an area. And a level that has changed sharply with no external explanation can indicate something about the well itself, such as a screen fouling or a casing problem, which is a contractor question. One reading is not a trend; a level measured at the same point in the season year on year is worth keeping.
Is a four gallon a minute well enough for a house?
For daily volume, comfortably — four gallons a minute is nearly six thousand gallons a day, several times what most households use. The question is never the daily total, it is whether the instantaneous rate covers peak demand, because two showers, a dishwasher and a washing machine at once can want more than four gallons a minute for a few minutes at a stretch. That is what a pressure tank partly absorbs and what storage absorbs completely. Rather than asking whether a rate is enough in the abstract, work out your peak simultaneous draw, compare it against the yield, and if the peak wins, put storage in between. That is what a low yield well always ends up doing anyway.