How this is calculated
The day’s water is the tested yield times 1,440 minutes. The household’s day is people times use per person, defaulting to EPA WaterSense’s 82 gallons per person at home, taken from the US Geological Survey’s 2015 water-use estimates, and to 124 liters in Europe, the EurEau 2022 figure quoted by the European Environment Agency.
The peak is a volume and a window. Over an event of V gallons in M minutes the well supplies yield times M, and the rest comes out of something already full when the tap opened.
The listed events are built from published fixture volumes: the federal 2.5 GPM showerhead flow, a standard clothes washer at 20 gallons a load and a dishwasher at 6.1, against 9.5 liters a minute, an efficient washer at 53 liters and a dishwasher at 12 in the Europe edition. The two-hour family peak is Penn State Extension’s own American example, carried across as a converted volume. Both numeric rows stay editable.
Casing storage is area times height: 0.0408 × d² gallons a foot for a diameter of d inches, so 1.47 at 6 inches and 4.08 at 10. The column runs from the static level to ten feet above the bottom, since the last stretch belongs to the pump intake.
The cistern figure is a day and a half of use rounded up to a tank you can buy, against Penn State Extension’s rule of thumb of 100 gallons per person, a full day as the target and two hours of peak use as the floor.
Worked example 1.5 GPM, four people, a 6-inch casing 400 feet deep with water 60 feet down. The well makes 2,160 gallons a day against 328 used. The column is 340 feet, 330 counted, and at 1.47 gallons a foot that is 485 gallons in the casing. A shower plus a clothes washer asks 40 gallons in 15 minutes against the well’s 22.5: a 17.5 gallon shortfall the column swallows. A 500 gallon cistern refills in 5.6 hours.
Worked example 5.7 liters a minute, four people, 150 mm casing 120 meters deep with water 18 meters down. The borehole makes 8,208 liters a day against 496 used. The column is 102 meters, 99 counted, and at 17.7 liters a meter that is 1,749 liters in the casing. A shower plus a washer asks 129 liters in 15 minutes against the borehole’s 85.5: a 43.5 liter shortfall. A 750 liter cistern refills in 2.2 hours.
Quick answers
Is 1 gallon per minute enough for a house?
For the day, easily: 1,440 gallons against the 328 a family of four uses. The peak is where it fails, and Penn State Extension’s family burns more than 300 gallons in two hours while a 1 GPM well delivers 120.
How much water is stored in a well casing?
1.47 gallons a foot in a 6-inch casing and 4.08 in a 10-inch, so 100 feet of water is 147 or 408 gallons. In metric, 17.7 liters a meter in a 150 mm borehole.
What yield do you need with no storage?
Penn State Extension suggests 6 GPM for most single-family homes and 18 for a six-bedroom, two-bathroom house. Those cover a peak from the well alone.
How is a yield test supposed to be done?
At a constant rate for at least 24 hours, or until the level holds for three consecutive half-hour readings, discharging away from the well. Most reported domestic figures are airlift readings over tens of minutes.
Does a low-yield well damage the pump?
Short cycling does. Franklin Electric caps encapsulated motors at 300 starts a day up to 3/4 HP and 100 single-phase from 1 to 5.5 HP, and asks a minimum one-minute run each time.
What a yield test measures
The number on a driller’s report is rarely the number a hydrogeologist would write down. The US Geological Survey, describing New Hampshire’s database of more than 20,000 reported bedrock wells, says yields “generally are determined as the rate of water that can be airlifted on a continuous, short-term (generally tens of minutes) basis.”
Tens of minutes is the problem. A 6-inch well holding 300 feet of water has 441 gallons in it before anything arrives from the rock. Blow that column out over 40 minutes, with the rock adding its 40 gallons, and the meter reads 12 GPM while the aquifer feeds 1.
A test that cannot be gamed pumps at a constant rate until the level stops falling: 24 hours without interruption, or three half-hour readings at the same elevation, discharging where the water cannot circle back. The owner’s version is a recovery test — pump the well down, stop, time the rise, and read feet per hour times gallons per foot as gallons per hour arriving from the rock.
The Survey adds a warning worth carrying into any report: yield is partly a function of demand, since “a well only is drilled as deep as is needed to meet a specific targeted yield.” A well reported at 5 GPM is often a well the driller stopped at 5.
One gallon a minute against six
Penn State Extension suggests a minimum of 6 GPM for most single-family homes, rising with bedrooms and bathrooms to 18 for six bedrooms and two bathrooms. That is a system with no real storage, where the well answers every tap on its own.
Peaks run 30 minutes to two hours, morning and evening, and a system has to cover two hours of them. Extension’s case is a Saturday morning of laundry, dishes, showers and toilets passing 300 gallons; a 1 GPM well brings 120 to that.
The pressure tank cannot close the gap, since only about 20 percent of its shell is usable water: 8 gallons out of 42, 24 out of 120. Hundreds of gallons are needed, which means an unpressurized tank.
Both thresholds are the same house. Six GPM buys one that needs no thought; 1 GPM buys it once a tank sits between the well and the pressure switch and the well spends the night refilling it.
Water stored in the casing
Every foot of standing water in the borehole is stored water, and widening or deepening a well buys more of it.
| Casing | Gallons per foot | 100 ft of water | 200 ft of water |
|---|---|---|---|
| 4 in | 0.65 | 65 | 131 |
| 5 in | 1.02 | 102 | 204 |
| 6 in | 1.47 | 147 | 294 |
| 8 in | 2.61 | 261 | 522 |
| 10 in | 4.08 | 408 | 816 |
| 12 in | 5.88 | 588 | 1,175 |
Computed from the cylinder volume at 7.48 gallons per cubic foot. The 6-inch and 10-inch rows match Penn State Extension’s published 147 and 408 gallons for 100 feet of water.
| Casing | Liters per meter | 30 m of water | 60 m of water |
|---|---|---|---|
| 100 mm | 7.9 | 236 | 471 |
| 125 mm | 12.3 | 368 | 736 |
| 150 mm | 17.7 | 530 | 1,060 |
| 165 mm | 21.4 | 641 | 1,283 |
| 200 mm | 31.4 | 943 | 1,885 |
| 250 mm | 49.1 | 1,473 | 2,945 |
Computed from the cylinder volume, 1,000 liters per cubic meter. A 150 mm borehole is the near equivalent of the American 6-inch casing at 17.7 liters a meter.
This store is the first thing a dry season takes. Extension’s warning is a well that normally stands with 100 feet of water and drops below 20 in a drought; at 20 feet, going from a 6-inch to a 10-inch hole buys about 52 extra gallons, which is one shower.
Deepening is steadier where the level swings, since another 100 feet of 6-inch hole adds 147 gallons wherever the level sits. It also opens the well to whatever the deeper rock carries, so the water needs retesting. Costs by depth and rock sit in the well depth and drilling cost atlas.
Cistern sizing and the two-pump arrangement
The standard fix is intermediate storage: two pumps with a tank between them. The well pump lifts water into an unpressurized cistern under a float switch, and a pressure pump takes water from the cistern to the pressure tank and the house.
The well pump is deliberately undersized, rated slightly below the well’s yield so it can run more or less continuously without pulling the level to the intake, with a low-water cutoff that overrides every other control before air or sediment reaches it.
Size the cistern for a full day at 100 gallons per person, so a family of five gets 500 gallons, and two tanks in parallel let you clean one while the other runs the house. Farm systems start at the US Department of Agriculture’s 2,000 gallon minimum. Anything not buried below the frost line lives in a heated space, and the tank doubles as chlorine contact and iron settling time.
Short cycling and the pump’s start budget
A submersible motor is cooled by the water moving past it, and every start dumps heat into the windings. Franklin Electric’s AIM manual sets the budget, and asks that motors run a minimum of one minute per start.
| Motor rating | Single-phase starts per 24 h | Three-phase starts per 24 h |
|---|---|---|
| Up to 3/4 HP (0.55 kW) | 300 | 300 |
| 1 to 5.5 HP (0.75 to 4 kW) | 100 | 300 |
| 7.5 to 30 HP (5.5 to 22 kW) | 50 | 100 |
Franklin Electric, AIM Manual for 60 Hz submersible motors, encapsulated types, 2026 edition. The manual also asks for at least 15 minutes between starts on 6-inch and larger encapsulated motors without a soft starter or drive.
Count the starts a real house makes. A 42 gallon pressure tank gives about 8 usable gallons, so 328 gallons a day is 41 starts; a 120 gallon tank with 24 usable gallons costs 14. The run-time rule bites hardest where a big pump meets a small tank: a 10 GPM pump emptying an 8 gallon drawdown runs 48 seconds, under the one-minute floor, every cycle of every day.
Intermediate storage fixes both numbers. The well pump runs long and rarely because it is filling a tank, and the pressure pump cycles without touching the well. Sizing the electrical side is what the well pump off-grid calculator is for, since the start-up surge is the load an inverter has to clear.
Hydrofracturing a rock well
When conservation, a cistern and a deeper hole have all been costed and the well still cannot fill a tank overnight, hydrofracturing is what is left. Packers seal off a section of the open borehole and water is pumped in at high pressure to flush and extend the fractures the well already crosses.
It is a bet on geology. The Survey’s New Hampshire work found reported yields from zero to more than 500 GPM, wells above 40 GPM at close to a tenth of the population, and the factors that moved yields were ones no owner controls: distance to surface water, the upgradient drainage area, valley bottoms against hilltops, and proximity to mapped fracture lineaments.
Hence the ranking. A well that passes on daily volume and fails on peak has a storage problem a tank solves for a known price, while fracturing is for the case where the daily volume itself is short and the result is unknown until the rig has been paid.
Sources
- Penn State Extension, Using Low-Yielding Wells (updated September 8, 2025): peaks of 30 minutes to two hours, the 300-gallon example, 20 percent of a pressure tank as usable water, 147 and 408 gallons per 100 feet of 6-inch and 10-inch casing, 100 gallons per person of cistern, the USDA 2,000 gallon farm minimum, and the two-pump arrangement with its low-water cutoff.
- Penn State Extension, Water System Planning: Estimating Water Needs and Before You Drill a Well (both updated May 29, 2025): 80 to 100 gallons per person a day, 6 GPM rising to 18, the two-hour peak, and constant-rate testing for 24 hours or three matching half-hour readings. The bedroom-and-bathroom flow rates are that page’s Table 2, taken from the Private Water Systems Handbook, 1992.
- US Geological Survey, Factors Related to Well Yield in the Fractured-Bedrock Aquifer of New Hampshire, Professional Paper 1660, 2002: airlift measurement over tens of minutes, 20,000-plus georeferenced wells, yields from zero to over 500 GPM, high-yield wells near 10 percent, and yield as a function of demand.
- Franklin Electric, AIM Manual for 60 Hz Submersible Systems, 2026 edition (M1311, June 2026): starts per 24 hours by rating, the one-minute minimum run, and the 15-minute gap for 6-inch and larger encapsulated motors.
- Fixture and per-person volumes. EPA WaterSense puts American home use at 82 gallons per person a day, from the Survey’s Estimated Use of Water in the United States in 2015, and states the standard showerhead flow as 2.5 GPM against its own 2.0 label. The 20-gallon standard and 14-gallon efficient clothes washer, and the 6.1-gallon standard and 3.2-gallon efficient dishwasher, are the ENERGY STAR and end-use-study volumes collected on the water numbers chart. Europe’s 124 liters a resident a day is EurEau’s 2022 figure, quoted by the European Environment Agency in Water Savings for a Water-Resilient Europe.
Go deeper
Once storage is settled the power question follows. Run the numbers through the well pump off-grid calculator for the start-up surge and the daily watt-hours a two-pump system asks of an inverter.
The water numbers chart holds the per-person and per-fixture volumes behind the peak events used here. Off-grid water storage sizing works through days of autonomy for the tank, and choosing an off-grid water source weighs the well against a spring, rain catchment and a haul.