Formulas For Water Supply Problems

USE OF FORMULAS TO SOLVE PROBLEMS
This appendix gives formulas for use in solving water supply problems often found in the
field. Each formula is accompanied by a problem solved by using the formula.
CONVERSION OF VOLUME TO WEIGHT OF WATER
The formula and a problem for conversion of volume to weight of water are given below.
a. Formula.
Weight of water in pounds = Cubic feet of water x 62.4
b. Illustrative Problem. What is the weight of water in a full tank with a volume of
470 cubic feet?
Weight of water = Cubic feet x 62.4
= 470 x 62.4
= 29,328 pounds
CONVERSION OF VERTICAL FEET OF WATER TO POUNDS
PER SQUARE INCH
The formula and a problem for conversion of vertical feet of water to pounds per square
inch
a.
b.
are given below.
Formula.
Pounds per square inch = Vertical feet of water x 0.43
Illustrative Problem. What is the pressure in pounds per square inch at the bottom of
a storage tank with 25 vertical feet of water? -
Pounds per square inch = Vertical feet of water x 0.43
= 25x 0.43
= 10.75
CONVERSION OF POUNDS PER SQUARE INCH TO
VERTICAL FEET OF WATER
The formula and a problem for conversion of pounds per square inch to vertical feet of
water are given below.
a. Formula.
Vertical feet of water= Pounds per square inch = 2.3
b. Illustrative Problem. How many vertical feet of water are in a tank that is 45 feet
high? A pressure gauge at the bottom of the tank reads 9 pounds per square inch.
Vertical feet of water = Pounds per square inch x 2.3
= 9 x 2.3
= 20.7

formula and a problem for conversion of volume to gallons of water are given below.
a. Formula.
Gallons of water= Cubic feet of water x 7.5
b. Illustrative Problem. How many gallons of water are in a tank with 400 cubic feet of
water?
Gallons of water = Cubic feet of water x 7.5
= 400 x 7.5
= 3.000
CONVERSION OF GALLONS OF WATER TO CUBIC FEET
The formula and a problem for conversion of water to cubic feet are given below,
a. Formula
Cubic feet = Gallons of water
7.5
b. Illustrative Problem. How many cubic feet of tank space are needed to store
1,500 gallons of water?
Cubic feet = Gallons of water
7.5
= 1,500
7.5
= 200
CALCULATION OF VOLUME OF WATER TANKS
The formula and two problems for calculation of volume of water tanks are given below.
a. Formula for Rectangular Tank
V= L x W x H.
where V = Volume in cubic feet
L = Length in feet
W = Width in feet
H = Height in feet
b. Formula for Cylindrical Tank.
V= p  r2H
where V = Volume in cubic feet
p = 3.14 or 22/7, a constant
r = Radius (half of the diameter) of the tank
H = Height in feet

c. Illustrative Problems. What is the volume of a rectangular tank that is 10 feet long,
7 feet wide, and 4 feet high?
V = L x W x H
= 10O x 7 x 4
= 280 cubic feet
What is the volume of a cylindrical tank that has a radius of 4 feet and is 7 feet high?
V= p r2H
= 3.14 x 42 X 7
=3.14 x 16 x 7
= 351.68 cubic feet
CALCULATION OF QUANTITY OF WATER FLOWING IN A STREAM
The formula and a problem for calculation of quantity of water flowing in a stream are
given below.
a. Formula.
Q = 6.4 x A x V
where Q = Quantity of water in gallons per minute
6.4 = Constant.
There are 7.5 gallons of water per cubic foot. However, because of error in
stream measurement, 7.5 is reduced to 6.4.
V = Velocity of the stream in feet per minute.
This figure is obtained by noting the time it takes a twig or floating object
to travel a known distance.
A = Area of the stream in square feet.
This figure is obtained by multiplying the width of the stream by the
depth of the stream.
b. Illustrative Problem. A stream has an average depth of 2 feet and a width of 16 feet. A
twig floats 13.3 feet per minute. How many gallons per minute are flowing in the stream?
Q = 6.4 x A x V
= 6.4 x 2 x 16 x 13.3
= 2,732.8 gallons per minute
CALCULATION OF POUNDS OF CHLORINE
The formula and a problem for calculation of pounds of chlorine are given below.
a. Formula.
Pounds of chlorine = Gallons of water x 8.3 x parts per million
1,000,000

b. Illustrative Problem. If eight parts per million of chlorine are required for
3,000 gallons of water, how many pounds of chlorine will be needed?
Pounds of chlorine = Gallons of water x 8.3 x parts per million
1,000,000
= 3,000 x 8.3 x 8
1,000,000
= 0.1992
CALCULATION OF GALLONS OF WATER THAT CAN BE
TREATED WITH A GIVEN SUPPLY OF CHLORINE
The formula and a problem for calculation of’ gallons of water that can be treated with a
given supply of chlorine are given below.
a.
b.
five
Formula.
Gallons of water =
Illustrative Problem.
Pounds of chlorine x 1,000,000
8.3 x parts per million
There are 4.15 pounds of chlorine on hand. The operator is using
parts per million of chlorine as the average treatment dosage. How many gallons of
water can the operator treat before running out of chlorine?
Gallons of water = Pounds of chlorine x 1,000,000
8.3 x parts per million
= 4.15 x 1,000,000
8.3 x 5
= 100,000
CALCULATION OF THE PARTS PER MILLION OF
CHLORINE PRESENT IN A TREATMENT TANK
The formula and a problem for calculation of parts per million of chlorine present in a
treatment tank are given below.
a. Formula.
Parts per million = Pounds of chlorine x 1,000,000
Gallons of water x 8.3
b. Illustratiue Problem. If 16.6 pounds of chlorine are added to 20,000 gallons of water,
how many parts per million of chlorine are present?
Parts per million = Pounds of chlorine x 1,000,000
Gallons of water x 8.3
= 16.6 x 1,000,000
20,000 x 8.3
= 100
CONVERSION OF POUNDS OF CHLORINE TO
OUNCES OF CALCIUM HYPOCHLORITE
The formula and a problem for conversion of pounds of chlorine to ounces of calcium
hypochlorite are given below.


a. Formula.
Ounces of calcium hypochlorite = Pounds of chlorine x 22.9
b. Illustrative Problem. If 1/2 pound of chlorine will be needed to treat a water source,
how many ounces of calcium hypochlorite will be required?
Ounces of calcium hypochlorite = Pounds of chlorine x 22.9
= 0.5 x 22.9
= 11.45