While some level of leakage is unavoidable, it is
important to SPU to keep leakage to a minimum because it represents a waste of
valuable resources and may result in water damage to property.
WDOH is developing a requirement that would limit
distribution system losses from all leaks to 10 percent of the total water
delivered to the retail service area. SPU intends to meet the
WDOH requirements with this service level. SPU's
water system has had a history of low leakage rates. In 2005, SPU's total non-revenue
water was 9.3 million gallons per
(mgd), or 7 percent of the total 128 mgd produced. Leakage is only one component of non-
revenue water; other components include seepage and
evaporation from open reservoirs, water used for flushing and firefighting, as
well as meter errors. Current leakage from SPU's
distribution and transmission system is estimated at
between 3.3 mgd and 4.8 mgd, or between 5 and 7 percent of the 67 mgd total
produced excluding that sold to wholesale customers in 2005.
Approximately 15 percent of the leakage comes from
transmission pipelines and water mains, and the remaining 85 percent comes from
service connections on SPU's side of the meter.
Maintaining adequate distribution system pressure is
critical to ensure both customer service and drinking water quality.
Adequate water pressure enables customers to have
sufficient water flow from their household plumbing fixtures and appliances.
In addition, adequate
pressure prevents contaminants from entering the distribution system through
pipeline leaks and cross connections. In 2004, SPU developed a service level
which meets Washington State Department of Health (WDOH) requirements for
pressure and provides a method for an economic analysis of supplying higher
pressure levels in new and existing areas of the distribution system. This
service level establishes a minimum 20 pounds per square inch (psi) service
connection pressure standard for the existing distribution system during normal
operations and a minimum 30-psi design standard for new distribution system
construction, consistent with the Washington Administrative Code (WAC). Current
services with less than 20 psi of pressure will be brought up to at least 20
psi through system improvements. Existing services with pressures less than 30
psi will be brought up to a higher pressure when it is economical to do so.