Attribute Related Measures: Infrastructure Stability

1. Asset inventory

Description: This measure gauges a utility’s efforts to assess assets and asset conditions, as the first steps towards building a comprehensive asset management program.

Example calculations:

  • Inventory coverage (percent): 100 X (total number of critical assets inventoried within a reasonable period of time (e.g., 5-10 years) ÷ total number of critical as­sets). A utility will need to first define what it considers to be a critical asset and a complete inventory will involve understanding the following for each:
    • Age and location;
    • Asset size and/or capacity;
    • Valuation data (e.g., original and replacement cost);
    • Installation date and expected service life;
    • Maintenance and performance history; and
    • Construction materials and recommended maintenance practices.[1]
  • Condition assessment coverage (percent): 100 X (total number of critical assets with condition assessed and categorized into condition categories within a reasonable period of time (e.g., 5-10 years) ÷ total number of critical assets). Condition cat­egories could include: unacceptable, improvement needed, adequate, good, and excellent to reflect expected service levels and accepted risks.

2. Asset (system) renewal/replacement

Description: This measure assesses asset renewal/replacement rates over time. The measure should reflect utility targets, which will vary depending on each utility’s determinations of acceptable risks for different asset classes. Decisions on asset re­placement typically factor in internally agreed-upon risks and objectives, which may differ by asset class and other considerations. For instance, a utility may decide to run certain assets to failure based on benefit-cost analysis.

Example calculations:

  • Asset renewal/replacement rate (percent): 100 X (total number of assets replaced per year for each asset class ÷ total number of assets in each asset class). For example, a two percent per year replacement target (50-year renewal) for a particular asset class could be identified as the basis for performance monitoring.


  • Asset (system) renewal/replacement rate: 100 X (total actual expenditures or total amount of funds reserved for renewal and replacement for each asset group ÷ to­tal present worth for renewal and replacement needs for each asset group). This is a QualServe Indicator.[2]

3. Water distribution/collection system integrity

Description: For drinking water utilities, this measure quantifies the number of pipe­line leaks and breaks. Distribution system integrity has importance for health, cus­tomer service, operational, and asset management reasons. For wastewater utilities, this measure examines the frequency of collection system failures. When tracked over time, a utility can evaluate whether its failure rate is decreasing, stable, or in­creasing. When data are maintained to characterize failures by pipe type and age, type of failure, and cost of repairs, decisions regarding routine maintenance and replace­ment/renewals can be better made.[3]

Example calculation (drinking water utilities):

  • Leakage and breakage frequency rate (percent): 100 X ((total number of leaks + total number of breaks) ÷ total miles of distribution piping per year). (Note: leaks and breaks are distinctly different events.) This is a QualServe Indicator.[4]

Example calculation (wastewater utilities):

  • Collection system failure rate (percent): 100 X (total number of collection system failures ÷ total miles of collection system piping per year). This is a QualServe Indicator.[5]

4. Planned maintenance

Description: Planned maintenance includes both preventive and predictive mainte­nance. Preventive maintenance is performed according to a predetermined schedule rather than in response to failure. Predictive maintenance is initiated when signals indicate that maintenance is due. All other maintenance is categorized as corrective or reactive.[6]

Example calculations:
This measure can be measured in different ways. Calculating costs may be preferable to encourage business decisions based on total cost; however, the reliability of costs is uncertain. Hours are likely to be less variable than costs, but not all utilities track hours. Thus, cost and hours ratios are desirable, where possible.

  • Planned maintenance ratio by hours (percent): 100 X (hours of planned maintenance ÷ (hours of planned + corrective maintenance)). This is a QualServe Indicator.[7]
  • Planned maintenance ratio by cost (percent): 100 X (cost of planned maintenance ÷ (cost of planned + corrective maintenance)). This is a QualServe Indicator.[8]

More information on resources for this attribute-related measure can be found in the EUM Resource Toolbox.

[1] From the U.S. General Accounting Office, Water Infrastructure: Comprehensive Asset Management Has Potential to Help Utilities Better Identify Needs and Plan Future Investments. GAO-04-461. March 2004. Available:
[2] From AWWA and AwwaRF, Selection and Definition of Performance Indicators for Water and Wastewater Utilities, p. 53. 2004. Note: This material is copyrighted and any reprinting must be by permission of the American Water Works Association.
[3] Ibid., p. 70.
[4] Ibid., p. 61.
[5] Ibid., p. 70.
[6] Ibid., p. 65.
[7] Ibid., p. 66.
[8] Ibid., p. 66.