Washington State and the Water Audit

May 4th 2018

The Washington State Department of Health is charged with protecting and improving the health of people in Washington State. To support this mission, the Department of Health addresses environmental health hazards associated with drinking water. Often, conversations about water-related health hazards focus on contaminants. But in Washington, public officials have recognized the relationship between water quantity and water quality and acknowledged that drinking water shortage is also an environmental health hazard. As a result, the Washington State Department of Health regulates water use efficiency right alongside water treatment protocols.

To ensure that water resources aren’t wasted at the expense of future generations, Washington drinking water suppliers are required to maintain distribution system leakage below 10% of supply, calculated as a three-year rolling average. To estimate annual leakage, the volume of authorized consumption is subtracted from the volume of supply, and the resulting volume is divided by the volume of supply to determine the system’s leakage percentage. Written symbolically, that’s:

DSL = [(TP – AC) / (TP)] x 100


DSL = percent of distribution system leakage (%)

TP = total water produced and purchased

AC = authorized consumption

If you’re versed in the American Water Works Association water audit methodology used to estimate leakage, you’ll notice something funky here – distribution system leakage includes apparent loss! Best-practice water audit methodology distinguishes between apparent (paper) loss incurred at the point of consumption (for example, due to customer meter inaccuracy) and leakage from distribution system infrastructure. These distinct water loss volumes carry different values and respond to different intervention strategies. As a result, accurately diagnosing a utility’s water loss volumes is essential for effective management. But as it’s currently employed, the Washington distribution system leakage calculation isn’t precise enough to allow for effective management.

Department of Health officials recognized this shortcoming but acknowledged that remedying it is not as simple as changing the state’s administrative code – utility professionals could benefit from technical assistance in integrating new methods and mandates. So, to study the introduction of water audit methodology in Washington, the Department of Health offered a pilot program to ten utilities.

The pilot program consisted of one-on-one technical assistance, a webinar, and a workshop, all geared toward the compilation and level 1 validation of a best-practice water audit assessing leakage. At the conclusion of each audit, the estimate of leakage was lower than the typical calculation of distribution system leakage because apparent losses were pulled out and recognized as a challenge distinct from leakage.

These results were further improved through level 1 validation. As instructors and validators, we worked with pilot participants to hone in on data quality, reasonable estimates for missing information, and the application of general methodology to each utility’s specific circumstances. The validation supported utility staff in trying on a new water accounting method for the first time, and we found that Washington water professionals are quick studies!

Most participants let us know that they prefer water audit methodology to Washington distribution system leakage calculations. According to one participant, “the water auditing process is much more informative than the traditional water use efficiency reporting… [and] the audit also provides focused suggestions where money and effort can be most effectively leveraged.” Bingo! We commend Washington Department of Health and utility professionals for their openness to new methods, and we’re excited for the water loss control journey that awaits the state.

Contact WSO

Fill out this contact form or email us at contact@wso.us for more information about our services!