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Well Flow Test: How to Do a Yield Test and What Numbers Pass

Last updated Reviewed by Sean Mihelich, founder of Save My Well

A well flow test runs the well without a break, often for four hours on a home sale, and records the gallons per minute every 15 minutes. A pass means the flow holds steady at the loan's number: FHA requires 3 gallons per minute from an existing well and 5 for new construction.

Step 1: read the well record first

The driller ran a yield test on the day the well was drilled, and the well log records it with the depth, the casing, and the static water level. The National Ground Water Association says that test helps forecast the well's long-term yield. Find the log in your state's well records, and compare it with today's result.

Step 2: set up a measured outlet

Run the water to the outside, through a hose or a discharge line, so it drains away from the well and the septic field. The Connecticut Department of Public Health (June 2009) describes the simple version for an older home: a licensed plumber or well driller puts a 1 to 10 gallons per minute water meter on the well's discharge line and runs the well to the surface until the flow stabilizes. With no meter, time how long a 5-gallon bucket takes to fill. Gallons divided by minutes is the flow: 5 gallons in 60 seconds is 5 gallons per minute.

Step 3: run the well and record every 15 minutes

Let the well run without a break for the full test, often four hours for a home sale. Every 15 minutes, write down the flow, whether the water is clear, and the water level if you can measure it. Watch for the warning signs: a falling flow, spurts of air, or sand and silt that grow worse. The worksheet below has a row for each reading.

Step 4: compare the result with the rule that applies

A pass means the flow held steady at or above the number the loan or the local code sets. For FHA, that is 3 gallons per minute of continuous flow from an existing well. Write the lowest steady reading on the report, not the first one, because the first minutes empty the casing and the pressure tank.

What flow rate passes?

Rule or guidanceFlowTest length
FHA, existing well3 gallons per minute, continuousNot set
FHA, new construction5 gallons per minuteAt least 4 hours
FHA, shared well3 gallons per minute for each home4 hours, continuous
Connecticut, new private wellSet by the well's required rateAt least 4 hours
Massachusetts, private wells (as of 2009)Not stated24 hours
Oregon State University guidance5 gallons per minute is adequateNot set
National Ground Water Association6 to 12 gallons per minute for most familiesNot set

Sources: the FHA rows are from HUD Handbook 4000.1, Update 18 (August 12, 2026). The Connecticut and Massachusetts rows are from the Connecticut Department of Public Health (June 2009), which adds that tests for new wells run from 1 to 24 hours by state and town, and recommends at least 18 hours for a well under 1 gallon per minute. The Oregon State University Well Water Program guidance was first written in 1999. The NGWA line is from its well log page, which says a well under 6 gallons per minute may need a storage tank.

How much water does a house need?

The Connecticut health department uses 75 gallons per person per day for private well design, so a house with 4 people needs about 300 gallons a day, and it counts 2 people per bedroom for larger homes. A low-yield well can still serve a house when storage makes up the difference: the department suggests extra storage tanks before drilling deeper, and notes that a 6-inch casing holds 1.5 gallons of water per foot.

Printable flow test worksheet

Print this page and fill one row every 15 minutes. Flow in gallons per minute equals gallons collected divided by minutes, or gallons times 60 divided by seconds.

Address: ____________________ Date: __________ Tested by: ____________________ Static water level before the test: __________

TimeGallonsSecondsGallons per minuteWater clear?Notes
0:00
0:15
0:30
0:45
1:00
1:15
1:30
1:45
2:00
2:15
2:30
2:45
3:00
3:15
3:30
3:45
4:00

What a flow test cannot tell you

  • The season. A test in a wet month can read higher than the well gives in a drought. The Oregon State University Well Water Program tells sellers who list in winter to keep a dry-season flow test on file.
  • The well beyond the pump. The test measures what the pump delivers. A small pump on a strong well shows the pump's limit. Only a well contractor can measure drawdown and recovery in the well itself.
  • The water quality. A flow test says nothing about bacteria. Take the lab sample at the end of the test, when the water comes from the aquifer and not from the casing; our well inspection checklist lists the tests to order.

What does a flow test cost?

The Well Guide (updated October 2026) says a well flow or yield test typically costs $200 to $600, depending on the pumping time and whether a water sample is included.

Well pros, inspectors, and agents

Inspectors, realtors and lenders: send your client the free well record and the free homebuyer report. For each loan's full well rules, see the FHA, VA and USDA well requirements.

Homeowner? Start with your well record. We look it up from your address.

Answer a few questions about your well. The kit is from $329, with a lidded mixing pail and a bacteria test before and after. For context, a professional treatment visit can cost up to $500, and it may not include a bacteria test.

Look up my well See what's in the kit

If the flow is fine and the well is short of water only in dry months, read signs a well is running dry.

Straight answers

What is a well flow test?

A well flow test, also called a yield test, runs the well continuously for a set time and measures how many gallons per minute it delivers and whether that rate holds. It shows whether the well and pump can keep up with a household. Home sales often use a four-hour test.

What is a good flow rate for a well?

HUD Handbook 4000.1 (Update 18, August 2026) requires at least 3 gallons per minute of continuous flow from an existing well for an FHA loan, and 5 gallons per minute over four hours for new construction. The National Ground Water Association says most families need 6 to 12 gallons per minute, with a storage tank below 6.

How long does a well flow test take?

Four hours is a common length for a home sale, and FHA uses four hours for new construction and shared wells. Connecticut requires at least four hours for a new private well, Connecticut's health department noted in 2009 that Massachusetts requires 24 hours, and Connecticut recommends 18 hours for a well under 1 gallon per minute.

How much does a well flow test cost?

The Well Guide (October 2026) says a well flow or yield test typically costs $200 to $600, depending on how long the well is pumped and whether a water sample is included. Many inspectors include it in a full well inspection for $250 to $400.

Can a well pass a flow test and still run dry?

Yes. A test in a wet month can overstate what the well gives in late summer, which is why Oregon State University suggests keeping a dry-season flow test on file. A flow test also measures what the pump delivers, so a small pump on a strong well shows the pump's limit, not the well's.

Is a flow test required for a home sale?

Only when the loan or the local code asks for it. FHA sets flow minimums, and many lenders ask for a flow test on a private well. Connecticut's health department says there is no yield test requirement for existing private wells there, so the contract and the lender decide.

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