Well Water Calculator
Recovery rate is the supply — the casing is just a buffer.
Work out Well Water. Recovery rate is the supply — the casing is just a buffer. Free, with no account and nothing to install.
From a sustained draw-down test, not a short one
11,520 L a day sustainable against 600 L needed
Meets demand
530 L stored in the casing · 480 L/h recovery
Storage in the casing is a buffer rather than a supply — what actually limits a well is the recovery rate. A well with a deep casing can pass a short flow test and still fail on a laundry day, which is why the sustained figure matters more than the first few minutes of a test.
How the Well Water Calculator works
Whether a well keeps up with household demand, separating the water stored in the casing from the rate it actually recovers. A deep casing can pass a short flow test and still fail on a laundry day.
Also known as: is my well enough for my house · well recovery rate calculator · well yield versus household demand · why does my well run dry in summer
Storage is a buffer, recovery is the supply
A well casing holds water — about 17.7 litres per metre of column in a 15 cm casing — and that water is a buffer for short peaks, not a source. Once drawn down, the well delivers only what it recovers.
Which is why a short flow test is misleading. Pumping for five minutes largely measures the casing, and a deep casing can pass a test that a genuinely slow well should fail. A sustained draw-down test over several hours is what measures the aquifer.
The daily figure that matters is recovery rate over 24 hours. Household demand is not spread evenly, so a well can meet the daily total and still fail during a morning peak — which is why both are checked here.
When the well cannot meet the peak
A storage tank between the well and the house is the standard answer. It fills steadily at whatever rate the well manages and then supplies a peak the well could never deliver directly, which converts a rate problem into a volume one.
It also protects the pump. Rapid cycling — starting and stopping repeatedly against a small pressure tank — is the main cause of well pump failure, and adequate storage removes it.
Seasonal variation is the case that catches people out. A well sized against winter performance can fail in late summer, when the water table is lowest and irrigation demand is highest. Testing at the driest time of year is far more informative.
Testing, and what a private well is not covered by
Private wells are rarely covered by public water monitoring, so testing is the owner's responsibility. Coliform bacteria and nitrates annually is a sensible baseline, plus anything the local geology suggests.
Arsenic, radon, fluoride and manganese are all region-specific concerns that will not appear unless specifically tested for. A local health department usually publishes what matters in the area, and that list is worth following rather than a generic panel.
Retesting after flooding, nearby construction or any change in taste, smell or clarity is the other half. A well that has been fine for a decade can change quickly when something upstream does.
Where to go next
The Well Water question rarely arrives on its own. These are the ones that usually come with it:
- Septic Tank Size Calculator — Sized on the greater of flow and bedrooms.
- Pump Head Calculator — Choosing on static lift alone is why pumps stall.
- Rain Barrel Calculator — One millimetre on one square metre is one litre.
- Ring Size Calculator — Finger measurement to US, UK, EU and Japanese sizes.
Frequently asked questions
How do I work out how much water my well can supply?
The sustainable figure is the recovery rate over 24 hours. Storage in the casing is a buffer for peaks, not a supply — once it is drawn down, the recovery rate is all there is.
What is a good well yield?
Enough to cover daily household demand with margin, which depends entirely on occupancy. What matters more is that the figure comes from a sustained draw-down test rather than a few minutes of pumping.
How much water does a household use?
Commonly 100 to 200 litres per person per day, varying enormously with fixtures, garden watering and habits. Your own metered history beats any average.
What if my well cannot meet peak demand?
A storage tank between the well and the house is the standard fix. It lets a slow well fill steadily and then meet a peak the well itself could never supply directly.
How is casing storage calculated?
The cross-sectional area of the casing times the standing water column. A 15 cm casing holds about 17.7 litres per metre of water column.
Why does my well run dry in summer?
Seasonal water table decline plus higher demand for irrigation. A well sized against winter performance can fail in late summer, which is why testing at the driest time is more informative.
How is a well yield test done properly?
By pumping at a constant rate for several hours while monitoring draw-down, then measuring recovery. A short test measures the casing storage rather than the well.
How often should well water be tested?
Annually for bacteria and nitrates at minimum, and after any flooding, nearby construction or change in taste. Private wells are rarely covered by public monitoring.
What contaminants should I test for?
Coliform bacteria and nitrates as a baseline, plus anything the local geology suggests — arsenic, radon, fluoride and manganese are all region-specific concerns.
Why does my well water smell of rotten eggs?
Hydrogen sulfide, usually from sulfur bacteria in the well or the water heater. Isolating whether it affects hot water only narrows it down quickly.
What is a pressure tank for?
It stores a small pressurised volume so the pump does not start for every tap. Undersizing causes rapid cycling, which is the main killer of well pumps.
Can a well be deepened?
Sometimes, though it may not reach a better aquifer and can introduce different water chemistry. A hydrogeologist's view is worth having before committing to the cost.
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