Altadena Water Hardness & Quality Report (2026)

Altadena, California, an unincorporated community in Los Angeles County north of Pasadena at the base of the San Gabriel Mountains — a historic and culturally significant Los Angeles County community known for Christmas Tree Lane (the oldest large-scale outdoor Christmas light display in the United States, on Santa Rosa Avenue, dating to 1920), a significant African-American middle-class community (one of the largest African-American middle-class communities west of the Mississippi in the 20th century), and a community of artists, academics, and professionals at the Pasadena–San Gabriel Mountain interface — draws its municipal water supply from the Raymond Basin and MWD import via Pasadena Water and Power (PWP). Water hardness in Altadena measures 95 mg/L — classified as moderately soft.

Altadena's moderate softness — significantly softer than most San Gabriel Valley communities — reflects the north Pasadena–Altadena distribution zone's effective treatment and geology. The Raymond Basin groundwater at Altadena draws from the San Gabriel Mountains alluvial fan (Quaternary alluvial deposits from the Cretaceous San Gabriel Mountains Batholith granodiorite — moderately calcareous). PWP applies effective treatment to blend the basin groundwater with MWD import, and Altadena's distribution zone receives the treated supply, producing the moderate 95 mg/L.

With hardness at 95 mg/L, Altadena residents enjoy moderately soft water. Pasadena Water and Power consistently delivers water meeting all California SWRCB and EPA Safe Drinking Water Act requirements.