How to measure the water level in your well
Static level, pumping level and recovery, and four ways to measure them. Updated October 3, 2026.
About 43 million people in the U.S. get their water from a private well, and the well's owner is the one who keeps an eye on it. The single most useful number is the depth to water: how far below the ground the water surface sits. Here's what to measure, and every practical way to do it.
The numbersElectric tapeChalked tapeAir lineSoundTotal depthSafety
The numbers that matter
- Static water level: the depth to water when the well has rested and nothing is pumping. Measure it after the pump has been off for a while, at least 30 minutes, and longer if you can.
- Pumping level: the depth to water while the pump runs. It's always deeper than the static level.
- Drawdown: pumping level minus static level. A big drawdown means the well gives up water slowly.
- Recovery: how fast the water climbs back after pumping stops. Fast recovery is a healthy, productive well.
- Measuring point: measurements are usually taken from the top of the casing. To get depth below ground, subtract how far the casing sticks up.
| Method | What you need | Cost | Good for |
|---|---|---|---|
| Electric water-level tape | A graduated tape with a probe that beeps at water | about $90–$700 | The standard; precise to a fraction of an inch |
| Chalked steel tape | Steel tape, weight, carpenter's chalk | under $50 | Shallow wells; a precise static level |
| Air line + gauge | An air line installed beside the drop pipe, a pressure gauge, a tire pump | varies | Repeated readings without opening the well |
| Sound (echo) | A sonic meter, or a phone app such as Well Sounder | app to pro instrument | Quick readings; nothing goes down the well |
1. Electric water-level tape
This is what well contractors and hydrologists use. A marked tape on a reel carries a small probe that completes a circuit when it touches water, and a light or buzzer goes off. Prices run from about $90 for a basic model to $675 or more for a professional one.
- Turn the pump off and let the well rest.
- Lower the probe through the access port or vent in the well cap. Some wells need the cap removed (see safety).
- When it signals, pinch the tape at the top of the casing and read the depth. Raise and lower it a few times to find the exact point.
- Pull it up slowly, keeping it clear of the pump wiring and drop pipe, and disinfect the probe before using it in another well.
2. Chalked steel tape (the "wetted tape" method)
An old, accurate method that needs no electronics. It works best when you roughly know the depth already.
- Coat the last few feet of a steel measuring tape with carpenter's chalk, and tie a small weight to the end.
- Lower it until a tape mark is at the top of the casing and the chalked end is below the water. Note the mark you're holding.
- Pull it up. The chalk shows a wet line.
- Depth to water = the mark you held − the length that's wet.
If you guessed wrong and the chalk is dry, lower it further and repeat. Use only clean tape and chalk; anything that goes down the well should be disinfected.
3. Air line and pressure gauge
Some wells have a thin tube (the air line) installed alongside the drop pipe, with its bottom end a known distance down, below the water. Pump air into it with a tire pump until the gauge stops rising: the pressure then equals the water above the end of the line.
feet of water above the end of the line = gauge reading (psi) × 2.31 depth to water = air line length − (psi × 2.31)Example: a 120 ft air line reading 30 psi has 30 × 2.31 = 69.3 ft of water over its end, so the water is 120 − 69.3 = 50.7 ft down. It's only as good as the length you know, and only works if the line is installed and airtight.
4. Sound: timing an echo
Sound sent down a well casing reflects off the water surface. Time how long the echo takes to come back and you have the depth:
depth to water = speed of sound × echo time ÷ 2Sound in air travels about 1,120 feet per second (it's a little faster when the air is warmer), so an echo that returns after 0.1 second means the water is about 56 feet down. Professional sonic water-level meters, such as the Solinst Model 104, work this way, with a built-in thermometer. Their maker notes they're most accurate in wells 8 inches across or less.
With a phone: Well Sounder does this with the iPhone's microphone (and, in Sweep mode, its speaker):
- It averages a dozen mallet taps to pull the echo out of the noise.
- It picks the water out of the other echoes, including the pitless adapter near the top and the joints in the drop pipe.
- It checks for the water's double echo.
- It corrects for the temperature of the air in the well.
Nothing goes down the well, and in Tap mode the cap stays on. Readings are estimates; temperature and obstructions in the casing affect them.
Coming soon to the App Store
"How deep is my well?" is a different number
The total depth of the well (where the drilling stopped) can't be found by sound or a water-level tape from the top: both stop at the water. It's on the well log (the driller's report). To find it:
- check your house paperwork, or a metal ID tag on the casing;
- ask the driller or your pump installer;
- search your state's well-log database. Many states put driller's reports online, searchable by address or location.
Total depth minus depth to water is the water column: the water standing in the well. A 6-inch casing holds about 1.5 gallons per foot of water column, and a 4-inch casing about 0.65 gallons per foot.
Safety
- Electricity: a submersible pump's power cable comes up through the well cap. Turn off the pump's breaker before you remove a cap or lower anything past the wiring.
- Contamination: keep the cap sealed and vermin-proof. Disinfect anything that goes into the well, and re-seal the cap afterwards.
- Casing: tap with a rubber or dead-blow mallet, never a steel hammer, and lightly on PVC.
- When in doubt, call a licensed well contractor, especially if the water is near the pump, the water changes colour or taste, or the cap or casing is damaged.
Keep a record
A single reading is a number; a season of readings is a story. Measure the static level at the same time of day, with the pump rested, every few weeks in a dry spell. A water level that keeps dropping is your cue to conserve, or to talk to a contractor before the pump runs dry.