Water Management Water is an important natural resource that requires proper management. Appropriate flow rate, pressure, and water quality are necessary for effective use.

Water System WATER SUPPLY STORAGE TREATMENT CONSUMER DISTRIBUTION

Supply

Treatment

Storage

Consumer 1 psi = 2.31 ft of water psi

Terminology Static pressure (head): No water flowing through the system Head loss: Pressure loss due to friction Actual pressure: Static pressure – head loss (all expressed in psi)

Hazen-Williams Formula hf = * L * Q 1.85 C 1.85 * d Where: hf = head loss due to friction (ft) L = length of pipe (ft) Q = flow rate of water through the pipe (gpm) C = Hazen-Williams constant d = diameter of the pipe (in.)

Water Supply Problem A business’s water supply connection at the street is at elevation 1,257 ft and has a pressure of 55 psi. The first floor fixture elevation is 1,285 ft. Between the connection and a first floor fixture, there are 120 ft of 3 in. copper pipe, 25 ft of ¾ in. copper pipe, and five (5) ¾ in o elbows. Discharge through the fixture is 10 gpm. The equivalent length for a single ¾ in., 90 o elbow is 4 ft. The Hazen- Williams constant for copper pipe is 140.

Water Supply Problem What is the pressure loss due to elevation change between the street connection and the first floor fixture? 1 st floor elevation – street elevation 1,285 ft – 1,257 ft = 28 ft Convert to psi: 28 ft ÷ 2.31 ft/psi = psi

Total Equivalent Length of ¾ in. Pipe = Pipe length + fitting equivalent length = 25 ft + (5 elbows * 4 ft/elbow) = ft

Head Loss in ¾ in. Pipe Friction head loss using Hazen Williams equation hf = * L * Q 1.85 C 1.85 * d hf = * 45 ft * (10 gpm) 1.85 (140) 1.85 * (3/4 in.) hf = ft

Head Loss in 3 in. Pipe hf = * L * Q 1.85 C 1.85 * d hf = * 120 ft * (10 gpm) 1.85 (140) 1.85 * (3 in.) hf = 0.05 ft

Total Head Loss for ¾ in. & 3 in. Pipe Total Head Loss (due to friction): = Head loss, ¾ in. pipe + head loss, 3 in. pipe = ft ft = ft Convert to psi: ft ÷ 2.31 ft/psi = 6.27 psi

Water Supply Problem What is the pressure in units of psi at the first floor fixture? Actual pressure = street pressure – static difference – head loss = 55 psi – psi – 6.27 psi = psi