Definition of well water static head height, total dynamic head and other volumes in well construction:

Here we define the static head in a well and we explain how the well's static head can compensate for a well with a poor flow rate.

The static head is basically a reservoir of water in the well bore or casing. It might be significant or trivial, but depending on your well bore recovery rate, the size of the static head can make the difference between a usable well with a low flow rate and running out of water. Also if you don't understand well static head you can be fooled by a "well flow test" result.

Static Head Height: Well Water Starting Quantity - What is the Static Head of Water in the Well?

This article series describes how we measure 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, artesian wells and well and water pump equipment.

How is well quantity measured? How do well static head volume, height, pressure vary over time?

Question: What happens to well flow when we install a more powerful water pump? Answer: We exhaust the well static head volume more quickly.

[Click to enlarge any image]

This sketch, courtesy of Carson Dunlop Associates offers a graphic explanation of well static head. The static head in a well is is not the total amount of water than can be pumped out of the well, it's just where we start.

 

Article Contents

• DEFINITIONS - WATER WELL HYDRAULICS
• STATIC HEAD VOLUME
• STATIC HEAD PRESSURE = PRESSURE HEAD
• STATIC HEIGHT = DISCHARGE HEAD
• HYDROSTATIC PRESSURE / BOTTOM HOLE PRESSURE
• TOTAL DYNAMIC HEAD
• STATIC LIFT = SUCTION HEAD
• HEAD LOSS = FRICTION LOSS
• CALCULATE WATER VOLUME per FOOT of WELL CASING
• TABLE OF WELL WATER VOLUME / QUANTITY per FOOT
• STATIC HEAD HEIGHT VOLUME CALCULATION
• VOLUME of WATER IN a PIPE - CALCULATION
• VOLUME of WATER IN a CYLINDER - CALCULATION
• WHY STATIC HEAD HEIGHT VOLUME CHANGES

Definitions of Static Head, Static Height, Static Lift, Total Dynamic Head (TDH) in a Well

Definition of Well Water Static Head Height or Static Well Volume

The static head volume (as used here) is the actual volume of water that is inside a well bore, cylinder or dug well when the well is at rest (not in use) and after it has fully recovered from prior or recent use.

The static head volume inside a water well tells us how much water is available to the pump after the well has rested, water has risen to its maximum height inside the well, and the pump is about to turn on.

As we will explain below, because (except in some flowing artesian wells) water does not rise all the way to the top of the well bore or dug well opening, the static head volume is less than the total volume of the interior of the well bore.

Definition of Static Pressure Head or Pressure Head

Static pressure head - the water pressure measured at the bottom of a column of water when the well is at rest and fully recovered. Static pressure head in this use could for clarity be called pressure head, or static head pressure.

The word "static" is important here. The pressure head at the bottom of the column of water in a well is strictly a function of the height of the water column (the diameter is irrelevant as you'll read in calculations later in this article).

When a water well is at rest and has fully recovered, the static head height, static head volume, and static head pressure or pressure head are all at their maximum.

Once a well pump begins running and the level of water inside the well bore is drawn down the height of the water column in the well as well as pressure head will be reduced.

As the pump continues to run the pressure head is not static but rather is dynamic, changing as the water level continues to drop.

What's the water pressure at the bottom of a well, as exerted by the column of water in the well?

Static head pressure: The PSI of water pressure at the base of a column of water of height H in feet = H x 0.433 psi

Pressure at the water well bottom increases by 0.433 psi per foot of height of water.

Example: If your well has a static head height of 100 feet, the water pressure at the bottom of that static head = static head pressure would be 100 x 0.433 = 43.3 psi.

Here's the math, simplified:

One 12x12" cube of water that is 12" high (one cubic foot) with a weight of 62.4 pounds (per cubic foot) exerts 62.4 psi over an area of (12x12) 144 square inches.

The psi (pounds per square inch) of force exerted by that cubic foot (a 12" high square of water) = 62.4 pounds / 144 sq.in. = 0.433 psi.

Only the height of the water column matters, not its diameter nor its shape. (And of course the force of gravity).

So a 1" tall column of water of any shape (including a round well bore) also exerts 0.433 psi as measured at the bottom of the column.

Details are at DEFINE WATER PRESSURE per FOOT of HEIGHT where we consider the weight of water. When at rest, the vertical pressure gradient in a column of water such as in a well bore depends only on the weight of the water.

Definition of Static Height or Discharge Head

A related but not identical well construction term of importance is

Static height, also referred to as discharge head: the maximum height that a pump has to lift water from the point of pickup.

Static height is typically higher than the static head (as used above) because the well water pipe in the well bore rises well above the top of the static water column to reach its exit point either at the casing top or at a pitless adapter from which piping continues onwards to the water destination.

If the well piping has to run uphill from the well exit to the building or to the water tank destination, that added height must be added to calculate the total static height accurately.

Definition of Hydrostatic Pressure (HSP) & Bottom Hole Pressure (BHP)

Hydrostatic pressure is defined as the pressure at the bottom of a well exerted by the weight of the column of water (or other fluid in the well) and is a function of the vertical height of the water column.

In a typical water well, bottom hole pressure (BHP) is identical to HSP and is the pressure exerted by water as measured at the bottom of the well.

BSP will be greater than the pressure exerted by the column of water at the point of water entry into the well piping at a foot valve or into the well pump at a submersible pump because those pick-up points are normally kept several feet above the actual well bottom.

 

Definition of Total Dynamic Head (TDH)

Really? As used by well drillers in describing well properties and in many textbooks cited in this article series, static head is used as we have defined it here.

Alternatively, in hydraulics, static head is sometimes used as a synonym for pressure head - the water pressure measured at the bottom of a column of water.

Static head in this use could for clarity be called pressure head, or static head pressure.

In fluid dynamics, Total Dynamic Head (TDH) is the total equivalent height that a fluid is to be pumped, taking into account friction losses in the pipe. TDH = Static Height + Static Lift + Friction Loss. - also written as

h_total = P2 - P1 / pg

Where

h_total is the total equivalent height that a fluid has to be lifted or pumped including taking into account the friction losses in the pipe

TDH is a measure of the amount of work that the pump must perform per unit of weight per unit volume of liquid. - Wikipedia https://en.m.wikipedia.org/wiki/Total_dynamic_head

Relation of TDH to Well Flow Rate

We will also have to include the rate at which water runs in to the well while we're pumping water out.

Looking at our rough well sketch below and repeated at Components of a Drilled Well with a Submersible Water Pump described

at WELLS CISTERNS & SPRINGS, and just considering the vertical arrows at the left side, we see that we have

• total well depth (d), which in more detail is comprised of
  • the air gap at the top of the well (a),
  • the pump clearance at the bottom of the well (c), and
  • the static head (h) which is the height of the column of water inside the casing which can be pumped out by the water pump when it operates.

Question: How to Calculate TDH Total Dynamic Head for a flowing artesian water well

2021/02/05 Zakaria Hofra said:

We have a new flowing artesian well, and we want to size the perfect pump for it.
What is the perfect pump (submersible or centrifugal) kind for it?

What is the best depth to install the pump?
How to calculate total dynamic head of the system in such case?

This Q&A were posted originally at PUMP, SUBMERSIBLE OPERATION

Moderator reply: example calcuation of total dynamic head for a flowing artesian water well

Zak

Thank you for the artesian well questions including the calculation of TDH total dynamic head.

You will see that without knowing specifics of your well such as its bore depth and the height of its water column, nobody can tell you its TDH or Total Dynamic Head.

As a mere example, if your artesian well is producing water flowing at a rate of 1 liter per second through a 1-inch diameter 200 foot long plastic pipe through which water rises a total of 100 feet, then the total dynamic head or TDH could be calculated as 40.24 meters (132.021 feet). ³.

For other readers, TDH or "Total Dynamic Head" in a water well is defined as the total pressure measured when water is actually flowing through a system, made up of the vertical rise-height of water and the friction loss through the system.

The friction loss will be a function of pipe diameter, material, and should include the effects of elbows and fittings too.

• TDH = static water height + static water lift + friction losses in the system
• TDH = the pressure difference between the pressure at the inlet and outlet of a well pump when that pressure is measured at the same height or elevation and when the inlet and outlet pipes or openings are of the same diameter.
• TDH = the height of column of water that is to be pumped out of a well bore.

In a practical sense we would treat TDH similarly to as Static Head in a water well, that we define and describe in detail on this page.

There, Zakaria, you'll find sketches and formulas for calculating the TDH or total dynamic head or static head.

A careful calculation of TDH or total dynamic head will also include the effects of Friction Loss, also referred to as Head Loss - the restriction on water flow due to friction of water against the piping surfaces as well as losses due to fittings such as elbows and valves.

Watch out: there is a difference between Static or Total Dynamic Head in a well - the column of water from top of water of a well at rest to the point of intake into the well pump or footvalve - and what other sources might call "static head" but that properly would be called

Static Lift: the total height that water rises between arriving at the water pump

Static Height: also referred to as Discharge Height: the total or maximum height from the outlet of a submersible pump to the point at which the piping turns horizontal to enter the building served.

The total amount of water from a conventional (not-artesian or not-flowing) well is the sum of the static head and the average flow rate or minimum flow rate of the well - the rate at which water flows into the well.

Watch out: there is no single "correct" flow rate for most wells. More-accurately, flow rates, whether for a non-flowing well OR even for an artesian well are never a single simple number like "GPM". The flow rate into a well bore varies seasonally as well as at various points along the depth of the well bore and is more-permanently affected by long term changes in the level of the water table that feeds the well.

Details are

at WELL YIELD DEFINITION where we describe the maximum amount of water one can get out of a well

For example, in areas of Guanajuato, Mexico, outside San Miguel de Allende, once a few large factory farm companies bought up farmland and began industrial-level farming of crops the rate of pumping of groundwater increased so dramatically (over the last 15-20 years) that the water table in that area dropped so percipitously that the older less-deep water wells used by local farmers dried-up and even trees in the area have all died from lack of water.

So, Zak, there is no possible single "right" or "best" generic answer to your question of the best depth at which to place your pump in an artesian well.

But in general, when using a submersible (in-well) water pump we put the pump 4-6 feet or a couple of meters above the well bottom. That gives us the maximum practical static head of water available to the pump while avoiding having the pump pick up sediment from the bottom of the well bore.

See more details

at WELL FLOW RATE

The flow rate of your flowing artesian well can and should be measured by the well driller: that's the rate of water naturally exiting the well before making any use of a well pump whatsoever. But as I warn above, that flow rate will vary over time and season and usage.

About your question of what is the "perfect pump", again I fear you're asking for Carnough the magician to give an answer to an un-answerable question. There is no perfect pump, since the best pump to use varies by individual well and water situation.

In general shallow wells use an above-ground 1 line jet pump;

Deep wells use a 2-line jet pump or a submersible pump;

You'll probably get maximum pumping capacity from a submersible pump.

ut

Watch out: if you try pumping water faster than the well's yield or flow-rate you'll simply exhaust the well and unless a pump protection device is installed you'll damage or destroy your pump.

Research on Total Dynamic Head

1. Wikipedia, "Total dynamic head", retrieved 2021/02/05 original source: https://en.wikipedia.org/wiki/Total_dynamic_head
2. Wikipedia, "Hydraulic head", retrieved 2021/02/05 original source: https://en.wikipedia.org/wiki/Hydraulic_head
3. WolflramAlpha, Total Dynamic Head Calculator: https://www.wolframalpha.com/input/?i=total+dynamic+head
4. March Pump, "How to Calculate Total Dynamic Head for an Industrial Pump" retrieved 2021/02./05 original source: https://www.marchpump.com/blog/how-to-calculate-total-dynamic-head-for-industrial-pump/#:~:text=15%20feet%20of%20vertical%20distance,feet%20of%20total%20dynamic%20head.
5. Hunter Industries, PIPE FRICTION LOSS TABLES [PDF] Hunter Residential & Commercial Irrigation,
   
   AUSTRALIA: Hunter Industries, Suite 7, 202 Ferntree Gully Road Notting Hill, Melbourne VIC 3168
   CHINA B1618, Huibin Office Bldg. No.8, Beichen Dong Street Beijing 100101 China
   
   EUROPE Avenida Diagonal 523, 5o-2a Edificio Atalaya 08029 Barcelona, SPAIN
   MEXICO Calle Nordika #8615 Colonia la Joya Tijuana, B.C., Mexico CP 22640
   MIDDLE EAST P.O. Box 2370 Amman,11941, Jordan
   
   " USA - Headquarters: Hunter Industries, 1940 Diamond Street San Marcos, CA 92078 USA,
   retrieved 2021/02/05, original source: https://www.hunterindustries.com/sites/default/files/tech_friction_loss_charts.pdf
   Excerpts [minor editing by InspectApedia]:
   
   STATIC PRESSURE: One foot of elevation change results in a change in static pressure of .433 psi.
   
   5 FACTORS in CALCULATING DYNAMIC PRESSURE in a piping system (when water is flowing) varies according to these following five factors, but is always less than static pressure for that same point.
   
   1. Velocity (of water–normally measured in feet per second)
   2. Inside Diameter (of pipe)
   3. Roughness (of inside wall of pipe)
   4. Length (of pipe)
   5. Change in Direction (such as elbows and tees)
   
   NOTE: This does not include remote control valves, backflow prevention devices, etc. The manufacturers' performance charts must be consulted for pressure loss information.
6. Pipe flow friction loss calculator, at http://www.freecalc.com/fricfram.htm
7. Washington State University, Total Dynamic Head Calculator, WSU Extension, "Irrigation in the Pacific Northwest", Prosser - IAREC, 24106 N Bunn Rd, Prosser WA 99350-8694, 509-786-2226, resource provided jointly to include Oregon State Univeristy Extension & University of Idaho Extension, retrieved 2021/02/05, original source: http://irrigation.wsu.edu/Content/Calculators/General/Total-Dynamic-Head.php
   Excerpt:
   
   "Head" is a word engineers use for pressure. This calculator determines the pressure (head) required just after the pump, and the pressure (head) that the pump must generate or add.
   
   The required pressure just after the pump (total dynamic head) includes pre-existing pressure of water entering the pump, pressure needed to overcome elevation differences (sometimes pressure is added if flowing downhill), and the pressure losses due to friction in the pipes in order to produce the required pressure at the emitters, or sprinklers.

 

Definition of Static Lift or Suction Head

For completeness and of more -interest to hydraulics engineers and well drillers is static lift.

Static lift is defined as the height that water must rise before arriving at the pump inlet.

Static lift in a well is the height of water in the well bore from the bottom of the well up to the point of water entry into the foot valve or into the submersible pump inlet.

Definition of Head Loss or Friction Loss

Head loss or friction loss is defined as the energy consumed by turbulence or friction inside the well casing and well piping during pumping.

Head loss in a well water system is a function of water pipe length, diameter, bends or elbows, fittings (whose edges form obstructions to water flow inside the pipe), and even piping material.

If your well piping contains many bends and fittings the effect is either more energy consumption to move water through the system or reduced water flow rate.

How to Calculate the Gallons of Water per Foot of a Well Casing

We have about 1.5 gallons of water per foot of depth of a well when we're using a standard residential 6" well casing. The height of water column inside the well and available to the pump is less than the total well depth.

[Click to enlarge any image]

With the exception of artesian wells, the well water column height does not extend from the well bottom to the top of the ground. Rather the top of the water in a conventional drilled or dug well at rest will be somewhere between the well bottom and well top, depending on the seasonal water table and other factors.

In an artesian well natural water pressures in the aquifer would force well water out at the top of the well casing.

For artesian wells the well is usually constructed with a seal inside the well casing to prevent water from rising above the point at which a water supply pipe exits the well casing. In an artesian well the static head water height will normally be from the well bottom to the point at which the casing seal has been installed.

Static head location in a well

In this sketch, distance (h) is the "static head" which is the total volume of water available to the pump.

The static head in a drilled well extends from the water intake at the pump (since water can't jump up to the pump intake) upwards to the highest point that water reaches inside the well casing when the well has rested and reached its normal maximum height.

Well water quantity calculation at pump startup

• (a) air in top of the well casing: water rises only to a height somewhere below the very top of the well.
• (h) static head: explained above
• (c) well bottom clearance: our well pump or foot valve (if the pump is not in the well) was placed 5' off of the well bottom © in the sketch, a distance to avoid drawing mud into the pump
• (d) total well depth: measured from the top of the ground to the bottom of the well. More about measuring the depth of a well is
  
  at DEPTH of a WELL, HOW TO MEASURE.

Table of Volume of Water in a Well or Pipe Per Foot or Meter

Notes to the table above

Notes:

Pipe diameters used here are the nominal or internal diameter or I.D. of the pipe.

The Static Head height or Actual Water Volume in the Well Bore is normally Less Than Total Well Bore Volume

The table above gives the volume of a cylinder (or well bore) of various diameters per foot of height or per meter of height.

Watch out: The volume of water inside of a well bore or well casing is normally less than the total volume inside the well bore cylinder.

The actual water volume is just for the portion of the casing that actually contains water when the well is at rest - don't count the air.

The portion of the well casing that is filled with water, or slightly more narrowly, the cylinder of water that extends from the pickup bottom point of the foot valve or submersible pump (the bottom of the usable water column) up to the top of the water column when the well is fully rested and recovered, is the well's static head.

The static head will generally be less than the volume of the whole well bore since water in the well does not rise to the top of the well bore.

Exception: the level of water in artesian wells will, if not deliberately blocked from doing so, rise to the top of the well bore.

1. Special thanks to readers Steven (October 17 2017) and Valerie (5 August 2017) for correcting our arithmetic errors.

2. 1 U.S. gallon contains 231 cubic inches

3. 1 Litre or liter contains 1000 cc's or cm³

4. 1 cubic foot contains 1728 cubic inches

The formulas for volume of a cylinder and thus of water in a well casing are shown and a examples are calculated below.

The Formula to Calculate the Static Head of Water in a Well

To find the amount of water in the static head of a well we find (h), the depth of the column of water in the well when the well is at rest, and then based on the well diameter we calculate the volume of (h) in cubic meters, feet, or inches. Last we convert that volume into common liquid measures such as liters or gallons.

Using the symbols and definitions given just above, the formula to express the size of the static head of water in a well first in feet of height is simply:

(h) = (d) - [(a) + (c)] - we subtract the well top air air space and pump to bottom clearance distances from total well depth

The actual water quantity in (h) is calculated based on the volume of the well cylinder interior.

In a standard 6" steel casing well, the water volume is about 1.5 gallons per foot of height of the static head

Formula for Static Head Volume in Gallons of Water in a Typical 6" Steel Well Casing

Static Head (h)_gallons = (1.5 gallons per foot) x (h) measured in feet

Here's a simple example to calculate the volume of water in the static head of a particular 100 foot deep well. Remember that for your well you'll need to plug in the actual measurements.

(d) = total well depth = 100 ft.

(a) = air in top of well casing = 45 ft.|

(c) = well bottom clearance between pump intake and well bottom = 5 ft.

We want to calculate (h), the static head, in gallons of water - we just need to calculate the height of the column of water (in feet) inside the 6" diameter well casing and multiply it by 1.5 (gallons per foot)

Static head water quantity (h)_gallons = (Total well depth (d) - Air (a) - Clearance at bottom (c) ) x 1.5

Or if you prefer

(h)_gallons = (h)_feet x 1.5

For this example, using the (d), (a), and (c) measurements from above, we calculate (h)_feet and multiply it by 1.5 to find the static head in gallons - (h)_gallons

(h)_gallons = [(100 - 45 - 5) feet of height of static head ] x [1.5 gallons per foot]

(h)_gallons = (50) x 1.5

(h)_gallons = 75 gallons of water - that's how much water is in the static head of the example well.

Static Head Height, Volume Measurements for Other Well Types

Note that the static head description and calculations given in this article apply to round drilled wells and round dug wells.

If your dug well is a different shape, say a rectangle, the principles are the same but you'll need to use the formula for volume of a rectangular shape V= length x width x height rather than a cylindrical shape given above and again just below.

The static head of a driven point well is practically zero - just the volume of water inside the lower section of the driven well point (a pipe) below ground. For a driven point well, if you still want to know its static head, you might try the calculation of volume of water stored in water piping, just below.

Calculate the volume a Cylinder, Tank, Well or Pipe

E.g. volume of water or gallons of water stored in water piping or in a well bore

In some circumstances such as deciding how much water to flush out of a pipe for certain water tests, it is useful to know the volume of water required to fill well piping or water piping.

But let's be clear - the volume of water resting in well piping does not increase the volume of water available at a property. That is, the water stored in well piping does not increase (nor decrease) the well's static head as we defined it above.

For long runs of well piping there may be a significant volume of water in the piping itself. Using 600' of plastic well piping as an example, we need simply to calculate the volume of a cylinder (the inside of a water pipe) into cubic inches per foot.

The volume of a cylinder V = pi x r² x h 

where pi = 3.1416,

r = cylinder radius (1/2 the diameter)

h = the cylinder height or length of pipe in our case and

G = the volume of water in U.S. gallons = 0.004329 gallons per cubic inch or more conveniently 1 U.S. gallon contains 231 cubic inches of liquid.

For U.K. readers,

G_U.K. = the volume of an imperial gallon is 277.419 cubic inches.

There is more water in long piping runs than one would have guessed.

To translate cubic inches of water inside of a pipe, 1 cu. in. is about 0.004329 gallons

• 1/2" internal diameter piping (that's a radius of 0.25") contains
  
  V = π r² h = π x 0.25² x 12 ≈ 2.35619 cubic inches

Divide the cubic inches by 231 (cu. in. per gallon)

G = 0.01 gallons per linear foot of pipe

• 3/4" internal diameter piping contains (.75/2)² x 3.1416 x 12 / 231 = 0.02 gallons per linear foot
• 1" internal diameter piping contains (1/2)² x 3.1416 x 12 / 231 = 0.04 gallons per linear foot

How to Calculate the Volume of Water Inside a Cylinder

The formula to calculate the volume of water in a cylinder is

Vcyl = pi x r² x h 

where

pi = 3.1416,

r = the radius of the circle formed by the cylinder (the well shaft or casing), and is simply 1/2 of the well diameter

h = the height of the cylinder of water (the static head height that we measured above).

Watch out! be sure to write the radius and height in the same units of measure - here we're going to use inches.

Vcyl_inches = 3.1416 x r²_inches x h_inches

So for a 12-inch (one foot) height of 6" diameter steel well casing,

r = the radius = 1/2 of the diameter of the pipe, or 3" and

h = the height is 12"

Now we can calculate the static head water volume in cubic inches:

Vcyl_inches= 3.1416 x 3²_inches x 12_inches

Vcyl_inches = 339.29 cubic inches (in this example, for a one foot high, 6" diameter cylinder of water in a well casing)

How to convert cubic inches to gallons

1 U.S. gallon contains 231 cubic inches

so for our 6-inch well casing that contains 339 cubic inches per foot,

339 / 231 = 1.4675 gallons per foot or about 1.5 gallons.

Alternatively:

How to convert cubic inches to cubic feet

Since there are 1728 cubic inches in a cubic foot (12 x 12 x 12) we divide:

Vc_feet = 339 / 1728

Vc_feet = 0.196 cubic feet

How to Convert Cubic Feet to Gallons

since 1 ft³ = 7.48051 gal(US Liq),

Vc_gallons = 0.196 x 7.4 = 1.46 gallons

That's why we use an easy to remember "rule of thumb" of 1.5 gallons per foot of static head of water found inside of a 6" drilled well casing.

Metric Calculation of Well Casing Volume

Using the formula for the volume of a cylinder

For a well casing that is 15cm in diameter and 1 meter in height:

Radius r = 1/2 the diameter or 7.5 cm

Vcyl = pi x r2 x h

Vc_{in cc} = pi x (7.5cm)2 x (100cm)

Vc_{in cc} = 3.1416 x 56.25cm [the bore radius in cm, squared] x 100cm [the bore height in cm) = 17,671 cc or cubic centimetres

1 cc = 0.001

1 m of a 15cm diameter well bore will contain 17.671 L - that would be the correct entry in our table

Water volume calculation for other metric well diameters:

1m of a 13cm well bore will contain 3.1416 x (13/2)² x 100 ccs [per L] = 1.1416 x 42.25 x 100 = 13,273 ccs or 13.2L of water per meter

1 m (or 100 cm) of a 20 cm diameter well bore will contain 3.1416 x (20/2)² x 100 ccs = 3.1416 x 100 x 100 = 31,416 ccs or 31.4L of water per meter

1 m of a 120cm diameter dug well will contain 3.1416 x (120/2)² x 100 ccs = 3.1416 x 3600 x 100 = 130,976 ccs or 130L of water per meter

Does the Static Head Quantity in a Well Change?

Absolutely. The static head, the amount of water in a well when the well is "at rest" - that is, no one has pumped water out of the well for some time and the well has filled back up as much as it's going to - changes:

• The well's static head will usually be at its lowest during the dry season of the year
• The water well's static head will usually be at its highest during the wettest season of the year, or after a period of heavy rainfall or heavy snow melt
• A well's static head may drop precipitously in response to events that disturb the soil or water bearing rock nearby, such as road or foundation blasting
• A well's static head may drop precipitously or even disappear entirely - leaving the well "dry" in response to changes in the underlying rock strata or on occasion if someone drills another water well nearby, tapping the same aquifer.

 

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2021-01-27 by (mod) - the static head is the actual height of the water column

Exactly right, YP the static head is the actual height of the water column in the well when the well is at rest and has fully recovered from any recent use.

Height and bore diameter allow calculation of the static head in gallons or liters.

We give those details above on this page.

On 2021-01-26 by Y. P. Sundriyal

if we have water level and depth of well can we calculate initial head?

On 2021-01-05 by (mod) - variations in current drawn by a water pump

Jerry

The current draw of a water pump will indeed be (perhaps only slightly) reduced in certain circumstances such as

When the pump's inlet or outlet pressure is restricted - lower pressure = less work = less current draw.

But

Watch out: as Terry Love points out, if you use a variable speed pump and you slow the pump speed you will actually use more total energy per gallon of water pumped.

Refrence:

Terry Love, "Variable speed pumps and energy uses" - original source: https://terrylove.com/forums/index.php?threads/variable-speed-flow-pumps-and-energy-usage.35009/
Excerpt:
Example;
1 HP pump at full speed puts out 10 GPM and pulls a full 1 HP load, which is 10 gallons per horse power.

When slowing down the RPM, the amps will drop by 50%. This is why so many people think, and can make you believe, they are saving energy. However, when slowed to 50% load, the pump is only moving 1 GPM, and using ½ HP load. That is only 2 gallons per horse power, or 500% more energy used when varying the speed of the pump.

So there is NO return on investment.

Really? Some readers reported making actual current draw (Amps) measurements using a variable speed pump and observing that the actual current draw at reduced output is only very slightly-reduced.

The current draw variation is absolutely bound to be quite different among water pump brands, models, and pump tpes.

VFD (Variable Frequency Drive) pumps may actually use more electrical energy per gallon when running at slower rates.

See

• WATER PUMP VARIABLE FREQUENCY / VARIABLE SPEED DRIVE (VFDs)

Also see

• CSIDesigns, HOW TO READ A PUMP CURVE, pump curve, pump calculator, centrifugal pump, positive displacment pump, Central States Industrial Headquarters 2700 N Partnership Blvd Springfield, MO 65803-8208 USA, Tel: 800 654 5635, retrieved 2021/02/05, at https://www.csidesigns.com/blog/articles/how-to-read-a-pump-curve

On 2021-01-05 by Jerry Steele

Thanks for the fast reply! Nice website by the way.

When measuring current draw of a well pump is it reasonable to assume that it is proportional to TDH, which is a measure of the amount of work that the pump must perform?

...

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