Maple Valley Water Hardness & Quality Report (2026)

Maple Valley, Washington, in King County, is served primarily by the Covington Water District, which draws its supply from the Cedar River Municipal Watershed — the same high-quality source that supplies the City of Seattle. The Cedar River originates in the Cascade Range at Chester Morse Lake, a reservoir high in the mountains south of Snoqualmie Pass, and flows west through a protected 91,000-acre watershed owned and managed by the City of Seattle Public Utilities. Covington Water District purchases treated Cedar River water and distributes it to Maple Valley and surrounding King County communities.

The moderately soft 78 mg/L hardness reflects the Cedar River watershed's geology. The Cascade Range here is dominated by Tertiary volcanic rocks — basaltic and andesitic flows — along with glacially polished metamorphic and granitic formations that have minimal carbonate content. Cedar River snowmelt and rainfall passing over these siliceous volcanic and igneous rocks accumulates relatively little calcium and magnesium. Some minor hardness arises from glacial till deposits in the lower valley and reservoir contact, but the overall profile remains comfortably soft.

At 78 mg/L, Maple Valley sits in the moderately soft range — excellent water quality for a Pacific Northwest community. Residents enjoy good soap lathering, minimal white film on dishes, and negligible scale formation in appliances over normal use periods. Light deposits may appear in kettles after several months of continuous use. Annual or semi-annual descaling keeps appliances in good condition. The primary water quality note for Maple Valley is the elevated lead at 0.009 mg/L — residents in older homes should flush taps briefly before drinking first-draw water and consider testing if pipes date to pre-1986 construction.