This article describes how a home owner or home buyer can test, measure, or estimate the amount of water available from a well and how to evaluate the water pressure delivered in a building served by a private well.
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The sketch at page top, courtesy of Carson Dunlop, outlines what happens during a true well flow test, also called a well drawdown or well flow test procedure. That procedure can give an accurate picture of how much water the well can deliver, though the quantity may vary seasonally or for other reasons.
But there are some steps that an amateur can take first to check on the well water quantity. In fact it's possible use mere visual inspection to form a reasonable suspicion that a building has insufficient well water before testing anything. We describe these procedures here.
What is a true well flow rate or capacity test?
At WELL FLOW RATE we explained that a real well flow rate test is usually performed right at the well by the well driller or a plumber, at the time the well was drilled, and using special equipment.
A true well flow test, well recovery test, or well draw-down test requires special equipment and locating, opening, and pumping right at the well. That procedure has the advantage that the well flow rate recorded is not affected by other problems such as a piping error or clogged water pipes or a defective well pump or water pressure tank.
A rough "do-it-yourself" well flow test
But when buying a property it's reasonable to perform your own crude water flow test right in the building, so long as you keep in mind that the water pump, water tank, pump controls, and the condition of the water supply piping, the height of the building, and the condition of the fixtures (such as a clogged sink spigot strainer) are all affecting the actual flow rate you see at a fixture. What we describe below is not a true well flow test or well drawdown test but this procedure can let us know early if there is an obvious red flag alert about water quantity.
The water flow rate at a building served by a pump and well will vary over time as the pump cycles on and off, and perhaps slow down or even stop completely if the well and its static head have only a limited volume of water available. The water pressure at a fixture served by a private well, pump, and pressure tank, will normally vary between the pump cut-in pressure (typically 20 psi or 30 psi) and the pump cut out pressure (typically 40 psi to 50 psi or a little higher).
If water pressure is always "ok" but varies between pretty strong and not so strong, this might be normal. Because the water pressure normally varies within this range, you may observe a modest change in water flow at an individual fixture such as a shower head or sink faucet.
If water pressure starts very strong and falls off to much slower immediately, we suspect a problem with clogged piping in the building: if the inside of a water supply pipe is blocked by mineral deposits or rust the effective diameter of the pipe is reduced, causing a reduction in water flow rate in a building even if the starting water pressure is good. Lots of people are confused about the difference between water flow rate (how many gallons per minute are coming out of a faucet) and water pressure (how hard is the water pressing inside the pipes and fixtures).
If water pressure drops way down to a very slow rate or stops entirely, there is a problem with the water pump, tank, piping, pump controls, or worst, there may be a problem with the well itself.
We explain how to diagnose loss of water pressure in detail at WATER PRESSURE LOSS .
Subjectively, we should be able to go to the highest bathroom or other plumbing facility in the building and run two fixtures simultaneously, seeing a reasonable water flow in which one could shower or wash. If you turn on the top floor shower and then open a sink faucet and you see the shower slow to a trickle, the building water pressure is unacceptable. If you couldn't reasonably bathe in a trickling shower flow, the flow is not functional. This usually not a water quantity problem, it's a pump, water tank, piping, or fixture problem. Usually. A well with a bad flow rate can also show up as a poor in-building water flow rate.
A typical bath sink faucet will flow around 1 gpm to 2 gpm, bath tub spout will flow at around 2.5 to 5 gpm, and a kitchen sink faucet at around 2-3 gpm. Low-flow water-saving fixtures may provide a good strong water stream but fewer gallons per minute.
Provided the home, community, and season are not in a time or area of drought and water shortage, it is reasonable to "waste" some well water for the benefit of the chance of discovery of a very important and costly water shortage at the individual well being tested. In some cases this test may be inappropriate (drought, already-failed septic field) or the owner may not permit it to be performed. If you cannot test water quantity or well yield you should not assume that you will have enough water at the property until you know more.
Calculate how many gallons of water you ran by adding up the individual fixture flow rates in gpm; multiply each fixture flow rate by the time it was running, and add up these numbers to get the total water volume we withdrew from the well.
Example of an amateur well yield test running three fixtures in a building:
Adding these up: Total Gallons of Water We Ran: 32+50+15 = 97 gallons total. Not much.
If our water supply system stopped dead with no water at the fixtures at the end of this test (we promptly turned everything off, including the pump when the water stopped flowing), our well gave us a total of 97 gallons before we ran dry.
If the well runs dry during modest use there is a problem: Even though this test is messy, if we run out of water we've got a clear, unambiguous result. We don't know how much of that 97 gallons was in the well's static head but we do know that unless we identify some other unusual problem (a broken pipe in the well or a failure of the pump itself) the well is inadequate. If this seat-of-the-pants well yield test runs out of water, there is a problem and you'll need to call in a plumber and perhaps a well expert to diagnose the problem before you know what steps need to be taken.
Watch out: if the water stops flowing, turn off the pump so it is not damaged by running dry and hot. See how long it takes for the well to recover enough for water to flow again when the pump is turned back on by trying it every half hour or so.
As our this Carson Dunlop sketch shows, a true well flow test, also called a well yield test or a well draw down test, is performed at the well, using a special pump which draws water directly from the well.
The inspector can vary the rate at which the pump draws water out of the well in order to determine the rate at which the well can deliver a sustained water flow rate or quantity over a measured time period, usually several hours, typically 3 hours or 4 hours, and in some cases over 24 hours.
A true well flow test or well draw down test will discover the ability of the well to deliver water, without confusion caused by the characteristics of the building's own well pump, pump control, water pressure tank, water piping, or fixtures.
All of these in-building components can dramatically affect water pressure and water flow rate in the building, and the size of the static head in a well can cause confusion between how much water is "available" at any given time and how much water the well can really deliver.
We explain these factors and other reasons why the true well yield number is complex
Because a true well flow test or well water draw down test requires that a special pump be attached directly to the well, this test is not normally performed during a pre-purchase home inspection. But this test should absolutely be performed if the inspection, building history, or other clues suggest that there may be a water quantity problem at the property.
Look around for other clues about water quantity: if you see lots of bottles of water stored near the water pump or water tank or even elsewhere in the building, if you see that flow restrictors are in use at every fixture, if you see a one line jet pump, any of these might be a clue that the well is unreliable or of limited capacity. Look for:
What about testing water flow and pressure from a well by using a flow gauge attached to a faucet? This is a "for show" measurement, not a real one - it is simply very inaccurate.
We can pretend to "measure" water flow, say at a tub spout, simply by seeing how many minutes it takes to fill the 5-gallon bucket. We can also pretend to "measure" water flow by attaching a flow meter gauge to a building faucet, typically to an outdoor spigot.
These tests are interesting but they're just pretending to measure the well - they're not really looking at the capacity of the well to deliver water. Instead this approach is really checking the capacity of the pump and piping to deliver a particular water flow rate and pressure
Lots of people do it, but we do not like nor trust most quantitative measurements of water flow at building fixtures because giving any quantitative number to such a flow is inaccurate. The flow at a plumbing fixture is set by the fixture itself, strainer, faucet, pipe diameter, pipe clogs, and by building piping and pump and water tank.
Furthermore, while we're running fixtures at a modest rate, the water pressure will cycle up and down between the pump cut-in and pump cut-out pressure. Since the actual water pressure is varying constantly, collecting and measuring the volume of water at a fixture during any short interval does not describe the full capability of the water supply system.
If the pump is not on we're not taking water out of the well: If water is being run slowly in a building, or perhaps just at one modest-flow fixture, the well pump will "catch up" with the demand, pressurize the water pressure tank, and the pump will turn off. The air spring in the water pressure tank keeps the water flowing out of the tank, but we're not taking any water out of the well during this part of the pump cycle.
When multiple building fixtures are running and we're taking lots of water out of the system, the well pump will usually run continuously. IF the well pump is running continuously, AND if it is not changing the pressure in the water pressure tank, then all of the pump output is going to the building fixtures and the sum of flow at all of them is probably a reasonable guess at the flow-rate capacity of the water supply system - that is, the capability of the well pump to send up water. We're still not checking the real capability of the well to deliver water - not until we connect a pump that is capable of pulling water out of the well faster than it flows into the well.
So we're not always testing the well yield when we're running the water - it depends on how fast we run the water and how long we run the water to determine if our test has even a slight chance of telling us about the actual well yield or well flow rate.
Flow Rate At a Fixture = (Time to fill the 5-gallon bucket in minutes) / 5 gallons
But faucet water flow rate is not the well flow rate - it's the flow rate of the pump and piping in the building. Don't let anyone fool you on this point. Even if we ran all building fixtures at once, kept the well pump running continuously, and measured all of the flows (to add them up) we still are only measuring what the pump is delivering, not how much water the well can provide.
Why do these pretend tests then? Because we might run out of water early - showing that there is indeed a well capacity or water quantity problem.
Not one of these measurements accurately describes how much water is available at the well. All we're seeing is whether or not the water system is producing functional pressure and flow rate; we're not seeing how much water is in the well.
So what can a home buyer or home owner do to estimate well yield before going to the cost and trouble of hiring a well-testing company for a true well draw down test or well recovery test?
Continue reading at WATER QUANTITY IMPROVEMENT or select a topic from the More Reading links shown below.
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Frequently Asked Questions (FAQs)
(June 11, 2011) M.Akram said:
(Mar 7, 2012) bryan said:
ask thr neighbors about the well and any problems they might have had with their well or if the previous owner had anny well problems. a;ways talk to the neighbord before buying and also the health department and a well drilling company tht may have worked that neighborhood.
(Jan 27, 2013) Dan said:
I have been doing the well flow..with a hose and, flow guage for 17 years and, never got a call back that the well went dry or, the test was not accurate so..the hose with the flow meter test works...period
Dan's hose and flow meter are of course not measuring well capacity nor flow rate, just a quantity delivered over his test interval, confounded by pumping rate and other variables. Useful but not a true well flow test.
why is my well water killign the leaves on my plants?
Anon, I don't see a question from you here. And I have no reason to think that potable well water kills leaves on plants. If you suspect your well water you should have it tested by a certified lab. For that matter private well water ought to be tested annually in any case.
Or you may be over-watering your plants, drowning them.
Question: well test costs
(Apr 4, 2014) lorraine said:
Any one knows what a quantity test for a well will cost in rural WA?
Well flow tests do vary widely by area and I don't have a figure for rural WA, but typically you can figure as much as $1200 or more for a true flow test.
Beware that short-cut tests may not be useful. To actually know a well's performance the contractor has to use a calibrated flow-rate pump at the well and pump for a specified time interval, possibly 24 hours, in order to be able to actually know the well's capacity.
If someone is charging you $50. and just stopping by to run water for five minutes, that might be measuring the flow rate of your pump and plumbing system by not the well capacity.
Question: well water problems in Spain Espana
(Apr 27, 2014) Jamas said:
I am a farmer from Spain. I will try to explain my problem, but sorry for my bad english.
I have a well for 2 years now, 7 meter, and with 2 meters of water. Last month i decided to digg more on this well, because i need more water for the plants and trees.
After 3 meters, i found hard rocky ground (stones). after 6 meters, under the rocks i found now black sand.
total meters: 10 + 6 meters of rock = 16 meters. And still not more water found.
Do i have to digg more, or do you think there is no more water. How can i explain this black sand? is this a sign for water or not?
any advice will be appreciated.
Gracias por la pregunta y explico que mi espan~ol no es perfecto tambien. No se si la arena negra significa que vas econtrar agua o no, pero es common que agua corre por arena por eso es posible.
Pero tambien hay peligro cavando muy profondo en un pozo por mano si no usas seguridad de una pared de cemento o piedra.
De que diametro esta el pozo. ?Si es ancho, sea posible cavar una cavacion mas fondo pero no ancho simplemente para buscar el agua?
Por favor, nunca trabajas solo.
(May 9, 2014) sylvie said:
I forgot to turn off the faucet outside it ran for at least 4 hours. Now i have gray water everywhere when I turn the water on. Is it possible to empty a well because of it? Will it fill back up? How long will it take?
Yes you may have run water so low in the well that you began picking up silt. Most wells will recover in anywhere from a few hours to overnight. If the silt problem continues you may need to flush the water tank and piping.
(May 22, 2014) Meme said:
My well pump goes on and off both approximately every 7 - 9 seconds. Is this ok? When faucets are open outside the pressure of the water increases and decreases according to the pump going on and off.
short cycling will burn up the pump
(July 28, 2014) Melanie said:
My pressure tank will drop pressure every 60 seconds with out the water being on. I have looked all over the house for leaks and cannot figure out why it looses pressure on it's own. because of this it is about to wear the relay out. Any suggestions?
A good diagnostic for the pump cycling you describe is at
Let us know if questions remain after you've seen that article.
Question: home seller does not want to permit a well flow test
9 Oct 2014 patti said:
My clients do not want a well inspection test done this time of year (Oct. in North Idaho) as the buyers have requested. My clients said when they do well tests and pump they run the well dry. Is that true?
A properly-conducted well test, if you're talking about a true flow test, might indeed "run the well dry" in which case the test has discovered a limit on the well's ability to deliver water.
What is very important is that the test person be on-site, paying attention. If the water supply stops, one must TURN OFF THE PUMP IMMEDIATELY to avoid possibly costly damage to the pump or its controls. Following that shut down one might also observe the necessary recovery time until water is again available, as that gives more interesting data about the well.
A sanity check on the procedure followed by the tester will include noticing just how much water the well delivered, over how much time. I'd want to know that data to protect against someone constructing a test that was unreasonable and thus did not give an accurate idea of the well's normal, in-use performance.
You've already been put on notice by their reluctance to permit a well test that this seller's well is probably of limited capacity - probably - else they'd not be worried about having a test performed. My OPINION (I'm not an attorney) is that this situation is just begging for a later dispute about fair and proper disclosure.
If I were selling this property I might however also be worried about some idiot flooding a septic system drainfield by running abnormal water levels into the wastewater system.
If I were buying this property and the sellers would not let me perform a normally-conducted property inspection or test I would have no choice but to assume that that component was not functional, and to consider that in deciding what I'd pay for the property.
However, in my opinion, it's rarely the case that a defect or repair should be a basis to abandon the purchase of a property: most repairs are a very small percentage of the total property value. Even needing to improve a well's yield or drill a new wall, which could certainly be several thousand dollars or more, should fall in that category.
Finally (well it's never really final, is it?)
the "well test" performed by many amateurs and some "pros" is not a true well flow test - which is done by well drillers and requires a special variable-rate pump, at the well, running for 24 hours to measure flow rates over that period. More often an inspector just runs some volume of water over some interval, or combines a flow test with a septic loading and dye test.
Those tests are not complete, do not give a true well flow rate, and are confounded by pump rates and other variables. But those tests CAN detect a well that runs out of water after delivering only a comparably small volume of water.
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