7.10 System Mapping, GIS, As-Builts, Operational Analysis & the AWWA Water Audit

You cannot operate what you cannot find

WPI lists "maintain an up-to-date map of the distribution system (GIS, repairs, replacements)", "interpret plans, maps, and system standard specifications", "perform operational analysis", "implement a water loss control program", and "understand elements of an asset management program" as distribution job tasks. They form one connected discipline: know what you have, measure what it does, and account for what is missing.

The record set

• System map or GIS. Every main with size, material, and installation year; every valve with type, size, turns to close, and direction; every hydrant; every service; every fitting and blow-off.
• As-built (record) drawings. What was actually installed, which is regularly different from what was designed. As-builts are produced at project closeout and are the source that updates the GIS.
• Valve and hydrant cards or asset records. Location tied to measured ties from permanent features, plus maintenance history.
• Standard specifications and details. The utility's requirements for materials, bedding, thrust restraint, tapping, disinfection, and testing, which contractors are held to.
• Hydraulic model. A calibrated network model used to evaluate fire flow, size mains, and plan zone changes.

GIS is a living record, not a project. Its value collapses if crews do not report what they actually find. Every repair, replacement, valve found in the wrong position, service line material identified during a dig, and abandoned line discovered must feed back into it. Mature utilities give crews a field data collection method — a tablet form, a marked-up print, or a GPS unit — and treat the update as part of closing the work order.

Operational analysis

"Analyze operational data, meet performance objectives, document operating conditions" is the WPI phrasing. The standing analyses are:

• Production versus consumption versus storage level, daily.
• Pressure at monitoring points across each zone under peak and minimum demand.
• Chlorine residual mapping across the system, which reveals stagnation and detention problems.
• Complaint mapping — plotting discolored water, taste and odor, and pressure complaints on the map almost always reveals a spatial pattern pointing at a dead end, an unlined main, or a zone boundary.
• Break history by pipe material, age, soil, and location, which drives replacement priority.

The AWWA water audit

Water loss control begins with a standardized accounting. The AWWA water balance separates the system input volume into components:

SYSTEM INPUT VOLUME (corrected for master meter error)
  |
  +-- AUTHORIZED CONSUMPTION
  |     +-- Billed authorized consumption  --> REVENUE WATER
  |     |     +-- Billed metered
  |     |     +-- Billed unmetered
  |     +-- Unbilled authorized consumption --> NON-REVENUE WATER
  |           +-- Unbilled metered (e.g., municipal buildings)
  |           +-- Unbilled unmetered (flushing, firefighting, street cleaning)
  |
  +-- WATER LOSSES                          --> NON-REVENUE WATER
        +-- APPARENT LOSSES (paper losses)
        |     +-- Customer meter inaccuracy (under-registration)
        |     +-- Systematic data handling and billing errors
        |     +-- Unauthorized consumption (theft, illegal connections)
        +-- REAL LOSSES (physical losses)
              +-- Leakage on transmission and distribution mains
              +-- Leakage and overflows at storage tanks
              +-- Leakage on service connections up to the meter

Two distinctions decide most audit questions:

1. Non-revenue water is not the same as water loss. Non-revenue water includes legitimate unbilled uses such as flushing and firefighting. A utility can have high non-revenue water and low actual losses.
2. Apparent losses are water that was delivered but not correctly recorded — under-registering meters, billing errors, theft. Real losses are water that physically escaped the system. The distinction drives the fix: apparent losses are corrected with meter replacement, billing audits, and enforcement, while real losses are corrected with leak detection and pipe replacement. Apparent losses are also worth more per gallon, because they are valued at the retail rate rather than at the production cost.

Performance indicators replace the obsolete "percentage unaccounted for," which is misleading because it varies with consumption. Current practice uses:

• Real losses in gallons per service connection per day, the primary operational indicator.
• Infrastructure Leakage Index (ILI), the ratio of current annual real losses to the unavoidable annual real losses for a system of that size, pressure, and connection density. An ILI of 1.0 is the technical minimum; well-run systems fall in the range of about 1 to 3.
• Apparent losses per service connection per day.

Every audit input carries a data validity score, which tells the utility where to invest in better measurement before chasing the number itself. The most common first finding is that the master meter has never been verified, which makes every downstream conclusion unreliable.

Worked example. A system with 4,200 service connections has an annual real loss volume of 62 million gallons.

Real losses = 62,000,000 gal/year ÷ 365 days ÷ 4,200 connections = 40.4 gallons per connection per day

That figure can be compared year over year and against peer systems in a way that a bare percentage cannot.