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WATER CALCULATION WORKSHEET
Information needed for water service sizing
I. U Demand of building in gallons per minute.
2. .2. Low pressure at main in street (or at external pressure tank).
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3. L Difference in elevation from main to meter (or external pressure tank to building control valve).
4. Y'f. Size of water meter (if applicable).
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5. ~ Developed length from main to meter (or external pressure tank to building control valve).
Your must first find the available pressure after the water meter (or at building control valve).
To obtain this pressure; you must:
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6. 6 L( Find pressure loss due to friction in I ff -inch diameter water service. pa1tlp! f.t rvL
7. () I J Find pressure loss due to elevation, main to meter (or external pressure tank to building control valve).
Multiply with difference in elevation by .434 psi/ft.
8. ~ Find pressure loss due to meter (from manufacturer or A WW A).
9. Lj /. L/ Subtract the loss due to friction (step 6), loss due to elevation (step 7), and loss due to meter (step 8) from the
low main pressure (or low pressure at external pressure tank (step 2). This calculation is the available
pressure after the water meter (or at the building control. valve). This answer is entered in Line B below.
Information needed for water distribution sizing
Using the following formula, find the pressure available for uniform loss (psi/IOO feet of pipe).
B -(C + D+E)
A= F X 100
WHERE:
A. ~ Pressure available for uniform loss (psill 00 feet of pipe).
B. Lj I.~ Available pressure after water meter (at the building control valve or low pressure at internal pressure tank)
(see step 9 above).
C. J 0 Pressure needed at controlling fixture.
D. ~ Differ~nce in elevation between water meter (building control valve or internal pressure tank) and controlling
fixture in feet ~ x .434 psi/ft.
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E. _ Pressure loss due to water softeners, water treatment devices, instantaneous water heaters and backflow
preventers which serve the controlling fixture. Conventional water heaters usually do not have a pressure
loss.
F. l~ Devel~ed length from water meter (building control valve or internal pressure tank) to controlling fixture in
feet ~ x 1.5. -
With pressure available for uniform loss, go to applicable table for distribution sizing.
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