Martha Lake Water Hardness & Quality Report (2026)

Martha Lake, Washington, in Snohomish County — an unincorporated Snohomish County community adjacent to Lynnwood and Bothell in the south Snohomish suburb of the Seattle metro — receives its water from the Alderwood Water and Wastewater District, drawing from Spada Lake Reservoir (Sultan River, Snohomish County) through the south Snohomish distribution.

The extremely soft 13.5 mg/L hardness and extremely low TDS of 20.4 mg/L are among the softest municipal water supplies in the entire USA — essentially distilled-quality water from the Cascade volcanic watershed. The Sultan River (Spada Lake Reservoir) drains the Cascade Range — Eocene Challis Formation (volcanic andesite and basalt — essentially insoluble), Jurassic metamorphic schist (insoluble), and Pleistocene glacial outwash (minimal mineral loading). The completely insoluble Cascade volcanic geology and high precipitation dilution produce the near-zero hardness and TDS at Martha Lake.

At 13.5 mg/L, Martha Lake's water is extremely soft — no scale forms whatsoever, soap lathers excessively, and appliances maintain perfect efficiency. No descaling is needed. The PFAS level of 1.3 ppt is very low — the Snohomish County south Seattle suburban corridor adjacent to the Sultan River Cascade watershed has essentially no major industrial PFAS sources, and the near-pristine Cascade watershed produces some of the cleanest PFAS readings in the dataset.