Page 39 - Water Loss Control

Understanding the Types of W ater Losses 21

• Background leakage: They are the collective weeps and seeps in pipe joints and
connections. They have flow rates that are typically too small (1 gpm (gallons
per minute) or 250 L/hr) to be detected by conventional acoustic leak-detection
equipment. They run continuously until they gradually worsen to the point
when they can be detected. The only ways of reducing background leakage is
through pressure management or infrastructure replacement.

Why Do Real Losses (Leakage) Occur
Real Losses exist in virtually every water-distribution network. They can never be com-
pletely eliminated and even newly commissioned sections of a network can have a
certain minimum volume of real losses (unavoidable volume of real losses). However,
how much the volume of real losses is in excess of the unavoidable minimum depends
on general characteristics of the distribution network and the leakage management
policy employed by the water utility.
The most common causes of leakage are

• Poor installation and workmanship
• Poor materials
• Mishandling of materials prior to installation
• Incorrect backfill
• Pressure transients
• Pressure fluctuations
• Excess pressure
• Corrosion
• Vibration and traffic loading
• Environmental conditions such as cold weather
• Lack of proper scheduled maintenance

Where Do Leaks Occur
In general, leaks can occur on three different sections of the network: transmission
mains (see Fig. 3.2), distribution mains (see Fig. 3.3), or service pipes (see Fig. 3.4).
Depending on where they occur they will have different characteristics such as flow
rate, tendency to cause supply interruptions, and likelihood to surface and be visible
above ground.
British leakage management terminology distinguishes reported versus unreported
leaks, or, more literally, reported bursts and unreported leaks. Dramatic pipe bursts are the
most recognizable example of a reported leak, which, due to their damage-causing
nature, are usually quickly reported, responded to and contained. However, unreported
leaks, often running at a small rate of flow on underground pipes, frequently escape the
attention of the water supplier and the public, but account for larger amounts of lost
water since they run undetected for long periods of time. Historically in the United States,
the terms reported and unreported are not employed, therefore the distinction between
a “leak” and a “break” (burst) is rather subjective, and is one of a number of examples
of inconsistent terminology. Efforts are underway in the United States, however to