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Drawdown test schematic for a water well (C) Carson Dunlop Associates used with permissionb at InspectApediaMeasure Well Depth: How Deep is the Well?
How to measure water well depth.

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How to measure well depth & how to abandon a well that will no longer be used.

How to use a string and weight to measure well depth. How much water is in the well?

Water quantity & definitions of well depth, water depth, static head, well volume, water quantity are explained

This article series describes how we measure the depth of a water well.

We caution that the amount of water available and the water delivery rate ability of various types of drinking water sources like wells, cisterns, dug wells, drilled wells, and even artesian wells is not answered just by measuring the depth of the well itself, but still we often need to know this number in order to know how to shock the well or how to prepare pipes, controls, and well pump choices or settings.



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How To Measure the Depth of a Water Well

Water well measurement details, Oregon Water Resources, at InspectApedia.comThe sketch at page top, courtesy of Carson Dunlop, outlines what happens during a well drawdown or well flow test procedure.

The illustration shown here explains that measuring water level in a well requires avoiding getting hung up on well piping, seals, spacers. Source: How to Measure Water Level in a Well, Oregon Water Department, cited below.

[Click to enlarge any image]

First you have to find the well. Second you need to know what kind of well is installed: driven point, drilled, or hand dug well, for example.

Two Key Questions to Ask About the Water Well

If you are purchasing a property served by a private well of any sort, here are the critical questions to ask about the well itself:

  1. Where is the well located? Is the well on the property? Can you find it? Sometimes there is a visible well casing above ground, or a visible protective cover over a dug well. Not always. If you can't find the well, see WELL LOCATION, HOW TO FIND.

  2. What kind of well is it: hand dug well, driven point well, drilled well, spring, stream, (these water source alternatives have implications for sanitation and water quantity as well as safety)

Measurements like the well depth, well flow rate, well recovery rate are all useful, but taken by themselves some of these numbers can give a false reading about the basic question of how much water is in the well?

What we ultimately need to know is the total quantity of water that can be drawn from the well and the quality of that water: is it potable, hard (mineral laden), smelly, dirty, requiring treatment for any aesthetic or health-concern contaminant?

See WELL FLOW RATE and see WELL FLOW TEST PROCEDURE.

Well Depth Measurement Tools, Devices, Procedures

Fishing float and string or fishing weight and string can be used to find the depth of a well and the top of the well water (C) Daniel Friedman InspectApedia.comTrimmer (1991) describes three methods to measure water levels in a well: an electronic sounder or depth gauge (device lowered on wire senses distance to water top), a wetted tape (accurate to about 90 ft), and an air line (measures anticipated usage volume not actual well water depth).

Here we describe several more-simple, very low-cost methods for making well and water depth measurements.

A simple steel egg sinker, 3/4oz or heavier can be used with string to find well depth. Adding a simple fishing float and suspending the weight just below the float can be used to find the depth to the top of well water. These fishing essentials are sold just about everywhere, including online at Bass Pro Shops (basspro.com). Here are the details:

How to Find the Depth of a Well using a simple String and Weight

I've used a simple float and weight to measure well depth and the depth to the top of the well water in well bores as well as dug wells.

The Water Ace Pump Company [cited at REFERENCES] as well as other water equipment companies like Flotec® offer a simple well depth measurement procedure that works for drilled wells or hand dug wells. We have added some details.

1. Tie a small but heavy weight to the end of a piece of string (be sure there is enough string; some wells are very deep). Lower the weight into the well until it reaches the bottom. I use a steel or magnesium fishing weight.

Watch out: be careful putting anything into your well, that you don't send down a weight that gets hooked on pipes or valves in the well bottom.

Use a small (non-lead-containing) fishing weight or a rounded object and tie it carefully. I don't use a lead weight because if I lose it I'll have to retrieve it: I don't want to leave a chunk of lead in the drinking water.

2. Take up the slack and mark the string at ground level. Pull the weight out of the well.

3. Measure from the bottom of the weight to the ground level mark on your string. This is the depth of your well.

For relatively shallow wells, 30' or less, we sometimes use a tape measure directly, but a weight on a string assures that the line used to make a measurement is absolutely straight, so more accurate.

How to Find the Level of Water Top the Well

Except for artesian wells, the top of the water level in the well will virtually always be some depth lower than the top of the ground surface.

As we explain below, there are reasons we want to know the depth from ground to the top of the water level in the well: to calculate the well's static head or volume.

Well Water Water Level by Observation

First be sure that the well is in fully-recovered mode. That means that no water has been drawn from the well (the pump is off or no water is being run at the building(s) served by the well for an interval long enough that the well has fully recovered.

Just how long you need to wait for a well to recover depends on the well's static head, and its flow rate or recovery rate. The time may be anywhere from a few minutes to 12 hours or longer.

If you can see the top of water in your well and if the top is not deep in the well, you may be able to measure to the water top using a simple tape measure.

Watch out: Take care not to drop the tape into the well, or tie a string from the tape's belt clip to your belt if you are clumsy like me.

Oops I dropped the weight into the well! Ok so have I. I also leaned over a well and dropped a fancy pen that my mom had given me. (I left it there and I never told anybody.)

See WELL PIPE RETRIEVAL TOOLS for help getting back stuff you've dropped into the well.

Well Water Level by Using a String & Fishing Float

If you cannot see the top of water in your well then you can tie a fishing float or "bobber" to your string and lower it carefully into the well until it stops dropping. Mark the string at ground level. Measure that string length - that's the depth from the ground surface to the top of your well water.

I hang a small light (non-lead) weight below my bobber to help lower it into the well and I take care to avoid snagging the bobber and string on components along the well pipe.

Well Water Level by Using a String & Water Finding Paste

You can adapt the string and weight method described above by adding a water finding paste to the upper portion of the string. Water finding paste will turn color (such as pink to blue) where it contacts water.

The string and paste will permit you to measure well depth and water top at once if you can first guess at the location of the water top so that you can locate where to put the paste without having to coat the entire string.

For a deep well I'd want a long, strong string, a smooth non-jamming weight.

Well Water Level Using a String and "Popper" (Pipe cap and nipple)

Flotec® describes using a popper or noise-maker assembled from a 4-6" x 1/2" pipe nipple and cap. The cap is sealed to the pipe nipple and the assembly is lowered into the well, again taking care not to snag the assembly in the well bore.

Flotec explains that when you lift the pipe nipple+ cap (open end down) from beneath the water surface back into the air the assembly will make a "pop" sound that is quite audible. Measure your string from ground level at that point to the bottom of the pipe nipple and you've measured the distance from ground level to top of the well water.

What do Well Depth Measurements Mean?

Well depth and well water depth permit you to calculate the static head or volume of water in the well at rest. These procedures are important for matching the well pump capacity to the physical depth of the well opening in the ground.

But knowing the well depth does not tell us much about how much water is actually in the well (though we can calculate that) and it doesn't tell us the rate at which we can take water out of the well and for how long - the well's flow rate.

Watch out: measuring the water level in a well is not the same as measuring well depth.

How to Find the End of the Steel Casing in a Well Bore

Reader Question: how do I measure the depth of the steel casing part of my well?

The current well casing is 6” steel and rusting, evidenced in the drinking water How do I determined the length of this casing? - J.D. 6/8/2013

Reply: string and magnet method; well camera method

My first preference in finding out details about a drilled well using a steel casing is to look in the building for notes about the well location, depth, and specifications; often the driller or plumber provides that data in writing and it may also be written on a wall or ceiling joist in a basement or crawl area where the well pipe enters the building, or at the water tank and well pump.

I've also had success calling local well drillers to find out who drilled the well as usually the company keeps well drilling record.

But if you are left with no information and need to know just the depth of the steel well casing (as opposed to the total well depth) try this procedure, working carefully to avoid dropping anything into the well or hanging up your cord and weight-magnet.

Watch out to avoid hanging the magnet up on the well pump, pipe connections, wiring. I like a round or cone-shaped magnet that is less likely to get caught up, and one that is just an inch or so in diameter;

Watch out: Don't drop stuff on the well.

An alternative is to hire a well service company who offer an inspection camera service. Such cameras are lowered into the well to inspect for casing cracks, rust holes, damage;

Matching Well Pump Capacity to Well Depth

Water Ace explains how to select the depth to which your submersible pump or foot valve should be placed in a water well.

Subtract five feet from the depth of your well. This number should not exceed the maximum rated depth for your pump. If it does, it will greatly hinder or prevent the proper operation of the pump.

FYI the five foot deduction from the physical well depth used to estimate pump capacity is assuming that the water pick-up end of your in-well piping will be held about five feet off of the physical bottom of the well. That's because placing the water pick-up too close to the very bottom of the well risks picking up silt and debris, clogging the foot valve, piping, and water pump

Well Depth Tools, Research, Articles, Methods

Well Abandonment / Bore-hole Sealing Procedures for Wells Taken out of Service

The steps you need to take to seal off a water well or to de-commission a well - this topic has been moved and expanded and is now found at WELL ABANDONMENT PROCEDURE

Readers of this document should also see WATER TANK TYPES and before assuming that a water problem is due to the well itself, see WATER PUMP REPAIR GUIDE an specific case which offers an example of diagnosis of loss of water pressure, loss of water, and analyzes the actual repair cost.

In a companion article, WELL FLOW TEST PROCEDURE, we describe both valid and questionable ways people measure well yield, and we offer some simple steps any home owner or home buyer can take to check the adequacy of water pressure and water quantity at a building.

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Continue reading at WELL LOCATION, HOW TO FIND or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see

How much water is in the well casing: STAIC HEAD of Water in the Well explains the role of water stored in the well casing or cavity itself and shows how to determine that volume.

More about measuring the actual depth of a well is at DEPTH of a WELL, HOW TO MEASURE.

How fast can we take water out of the well: WELL YIELD DEFINITION - explains how well yield or well flow rates are measured, provides formulas, and an example of calculations

How much water can we get from the well: WELL QUANTITY TOTAL - explains the true volume of water that is available from a given well, the role of the static head, the flow rate, the pumping rate, and factors that affect well life and changes in well yield.

Suggested citation for this web page

WELL DEPTH, HOW TO MEASURE at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

INDEX to RELATED ARTICLES: ARTICLE INDEX to WATER SUPPLY, PUMPS TANKS WELLS

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