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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. 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. The sketch at page top, courtesy of Carson Dunlop, shows how the static head of water in a well is located and estimated. Details are below.

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 and pressure tank repair diagnosis & cost 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, How to Test Well Water Quantity, 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.

© Copyright 2012 InspectAPedia.com, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use page top links to major topics or use links at the left of each page to navigate within topics and documents at this website. Green links show where you are in a document series or at this website.

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

Calculating the gallons of water per foot of 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. Except in artesian walls the water column does not extend from the well bottom to the top of the ground.

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 very bottom of the pump (since water can't jump up to the pump) 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.

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

But remember that's just for the portion of the casing that actually contains water when the well is at rest - don't count the air. The formulas for volume of a cylinder and thus of water in a well casing are shown and an example are calculated just below.

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 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 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.

Formula for Static Head 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 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.

Calculating the volume of water or gallons of water stored in water piping

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) and

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

G = the volume of water in gallons = 0.004329 gallons per cubic inch

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 contains 2.35 cubic inches or (2.35 x 0.004329) = 0.01 gallons per linear foot:
  .5 / 2 = r = .25", and h = 12" per foot,
  V = (.25)² x 3.1416 x 12 = 2.36 cu. in. per foot. Multiplying this by 0.004329 we obtain
  G = 0.01 per linear foot of pipe
• 3/4" internal diameter piping contains (.75)² x 3.1416 x 12 x 0.004329 = 0.02 gallons per linear foot
• 1" internal diameter piping contains (1)² c 3.1416 x 12 x 0.004329 = 0.04 gallons per linear foot

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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• Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. Thanks to Alan Carson and Bob Dunlop, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education including the ASHI-adopted Home Inspection Training Program (home study course), publications such as the Home Reference Book, report writing materials including the Horizon report writer, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.

Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

WELLS CISTERNS & SPRINGS
  AIR DISCHARGE at FAUCETS, FIXTURES
  Basement Wells
  CHECK VALVES
  CISTERNS
  DEPTH of a WELL, HOW TO MEASURE
  Drilled Wells - steel casings
    Drilled Well with Submersible Pump
    Shallow Well with One Line Jet Pump
    OLD WELL - RETURN TO SERVICE
    Well with Two Line Jet Pump
  Driven Point Wells
  How Much Water is In the Well?
    Static Head of Water in the Well
    Well Yield: Well Flow Rate
    Total Quantity of Water Available
  How to Test Well Water Quantity
  How to Get More Water From a Well
  Hand Dug Wells
  Hand Dug Well Procedure
  Jetted Wells
  OLD WELL - RETURN TO SERVICE
  Springs as Water Supply
  Wash Wells
  Well Pits
  WATER HAMMER NOISE DIAGNOSE & CURE
  WATER PRESSURE LOSS
  WATER PUMP SAFETY
  WATER TANK SAFETY
  WATER TANK TYPES
  WELL CHLORINATION SHOCKING PROCEDURE
  WELL CLEARANCE DISTANCES
  WELL DEPTH, HOW TO MEASURE
  WELL FLOW RATE
  WELL LIFE EXPECTANCY
  WELL PIPING CHECK VALVES
  WELL PIPING FOOT VALVES
  WELL PIPING LEAK DIAGNOSIS
  WELL PIPING TAIL PIECE
  WELL PUMP PRIMING PROCEDURE
  WELL PUMP TYPES & LIFE EXPECTANCY
WELL CHLORINATION SHOCKING PROCEDURE

• Thanks to reader Alan Starkman, Oaxaca, Mexico, for discussing well flow rate calculations 2/17/2010.

Water Supply & Drain Piping, Wells, Pumps, Water Supply Equipment

• Access Water Energy, PO Box 2061, Moorabbin, VIC 3189, Australia, Tel: 1300 797 758, email: sales@accesswater.com.au Moorabbin Office: Kingston Trade Centre, 100 Cochranes Rd, Moorabbin, VIC 3189
  Australian supplier of: Greywater systems, Solar power to grid packages, Edwards solar systems, Vulcan compact solar systems, water & solar system pumps & controls, and a wide rage of above ground & under ground water storage tanks: concrete, steel, plastic, modular, and bladder storage tanks.
• Cheating on water tests: Testing Water for Real Estate Transactions - make sure your water test is valid
• Diagnosing Clogged Drains: Is it a blocked drain or the septic system? - A First Step for Homeowners
• Drinking Water Contaminant Levels - Maximum Allowed
• Drinking Water Supply, Contamination Levels, Water Testing Procedures
• Drinking Water Testing Advice for home buyers home owners home inspectors
• Interpreting Drinking Water Test Results and Correcting Unsatisfactory Water
• Lead Contamination in Drinking Water: Testing & Correction - Advice (This Article)
• Lead Testing & Correcting Contamination from Lead Water Supply Lines/Entry Mains - Lead Pipe Problems/Advice
• Life Expectancy of Water Pumps - Well Pumps: how long should a water pump last? What affects pump life?
• Life Expectancy of Wells & Water Tanks how long should a water well and its components last?
• Plumbing Diagnosis & Repair: Water supply, drainage, septic systems, water testing, water contamination, defective plumbing materials & products.
• Shock or Chlorinate a Well, How to - Procedure for Shocking a Well to (temporarily or maybe longer) "Correct" Bacterial Contamination
• Smart Tank, Installation Instructions [ copy on file as /water/Smart_Tank_Flexcon.pdf ] - , Flexcon Industries, 300 Pond St., Randolph MA 02368, www.flexconind.com, Tel: 800-527-0030 - web search 07/24/2010, original source: http://www.flexconind.com/pdf/st_install.pdf
• Typical Shallow Well One Line Jet Pump Installation [ copy on file as /water/Jet_Pump_Grove_Elect_Jet_Pumps_1.pdf ] - , Grove Electric, G&G Electric & Plumbing, 1900 NE 78th St., Suite 101, Vancouver WA 98665 www.grovelectric.com - web search -7/15/2010 original source: http://www.groverelectric.com/howto/38_Typical%20Jet%20Pump%20Installation.pdf
• Typical Deep Well Two Line Jet Pump Installation [ copy on file as /water/Jet_Pump_Grove_Elect.pdf ] - , Grove Electric, G&G Electric & Plumbing, 1900 NE 78th St., Suite 101, Vancouver WA 98665 www.grovelectric.com - web search -7/15/2010 original source: http://www.groverelectric.com/howto/38_Typical%20Jet%20Pump%20Installation.pdf
• Water Fact Sheet #3, Using Low-Yielding Wells [ copy on file as /water/Low_Yield_Wells_Penn_State.pdf ] - , Penn State College of Agricultural Sciences, Cooperative Extension, School of Forest Resources, web search 07/24/2010, original source: http://pubs.cas.psu.edu/FreePubs/pdfs/XH0002.pdf
• Water pressure tanks - how to diagnose the need for air, how to add air, stop water pump short cycling to avoid damage - water storage water pressure tank safety.
• Water pump and pressure tank repair diagnosis & cost an specific case offers an example of diagnosis of loss of water pressure, loss of water, and analyzes the actual repair cost
• Water pressure tank failures & water pump short cycling diagnosis and repair
• Water Supply & Drain Piping, water and drain pipe types, inspection, diagnosis, repairs, problem materials, clogging, etc.
• Water Tests & Fees this water test fee schedule applies when testing is combined with other onsite building inspection services
• Water Testing: background comments on classes of water contaminants, & links to home buyer advice about water testing, drinking water, water supply
• Water Requirements, Home & Outdoor Living

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

• Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop, and from the InspectAPedia bookstore. The 2010 edition of the Home Reference Book is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. InspectAPedia.com ® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.

• Crystal Clear Supply provides portable ceramic water filter purifiers and portable reverse osmosis water treatment equipment - see http://www.crystalclearsupply.com/category_s/7.htm
• Handbook of Disinfectants and Antiseptics, Joseph M. Ascenzi (Editor), CRC, 1995, ISBN-10: 0824795245 ISBN-13: 978-0824795245 "The evaluation of chemical germicides predates the golden age of microbiology..." -
  This well-focused, up-to-date reference details the current medical uses of antiseptics and disinfectants -- particularly in the control of hospital-acquired infections -- presenting methods for evaluating products to obtain regulatory approval and examining chemical, physical, and microbiological properties as well as the toxicology of the most widely used commercial chemicals.
• Potable Aqua® emergency drinking water germicidal tablets are produced by the Wisconsin Pharmacal Co., Jackson WI 53037. 800-558-6614 pharmacalway.com
• Principles and Practice of Disinfection, Preservation and Sterilization (Hardcover)
  by A. D. Russell (Editor), W. B. Hugo (Editor), G. A. J. Ayliffe (Editor), Blackwell Science, 2004. ISBN-10: 1405101997, ISBN-13: 978-1405101998.
  "This superb book is the best of its kind available and one that will undoubtedly be useful, if not essential, to workers in a variety of industries. Thirty-one distinguished specialists deal comprehensively with the subject matter indicated by the title ... The book is produced with care, is very readable with useful selected references at the end of each chapter and an excellent index. It is an essential source book for everyone interested in this field. For pharmacy undergraduates, it will complement the excellent text on pharmaceutical microbiology by two of the present editors."
  The Pharmaceutical Journal: "This is an excellent book. It deals comprehensively and authoritatively with its subject with contributions from 31 distinguished specialists. There is a great deal to interest all those involved in hospital infection ... This book is exceptionally well laid out. There are well chosen references for each chapter and an excellent index. It is highly recommended." The Journal of Hospital Infection.: "The editors and authors must be congratulated for this excellent treatise on nonantibiotic antimicrobial measures in hospitals and industry ... The publication is highly recommended to hospital and research personnel, especially to clinical microbiologists, infection-control and environmental-safety specialists, pharmacists, and dieticians."
  New England Journal of Medicine: City Hospital, Birmingham, UK. Covers the many methods of the elimination or prevention of microbial growth. Provides an historical overview, descriptions of the types of antimicrobial agents, factors affecting efficacy, evaluation methods, and types of resistance. Features sterilization methods, and more. Previous edition: c1999. DNLM: Sterilization--methods.
• U.S. Army Field Manual 21-10, Field Hygiene and Sanitation, 1988, web search 07/02/2010, original source: http://www.enlisted.info/field-manuals/fm-21-10-field-hygiene-and-sanitation.shtml
  The purpose of this manual is to assist individual soldiers, unit commanders, leaders and field sanitation teams in preventing disease and environmental injuries. The manual provides information on preventive medicine measures (PMM) to the individual soldier as well as essential information for the unit commander, unit leaders, and the unit field sanitation team on applying unit level PMM.
• When Technology Fails, Matthew Stein, Chelsea Green Publisher, 2008,493 pages. ISBN-10: 1933392452 ISBN-13: 978-1933392455, "... how to find and sterilize water in the face of utility failure, as well as practical information for dealing with water-quality issues even when the public tap water is still flowing". Mr. Stein's website is www.whentechfails.com/
• ...