Monterey Park Water Hardness & Quality Report (2026)

Monterey Park, California, in the western San Gabriel Valley adjacent to East Los Angeles — one of the first suburban cities in the United States to have a majority Asian-American population (predominantly Chinese-American), dubbed 'Little Taipei' and 'the first suburban Chinatown' — draws its municipal water supply from the Raymond Basin groundwater and Metropolitan Water District (MWD) imported water via the City of Monterey Park Public Works Water Division, accessing the Raymond Basin (the Pasadena–Alhambra–Monterey Park sub-basin of the San Gabriel Valley Groundwater Basin). Water hardness in Monterey Park measures 49 mg/L — classified as very soft.

Monterey Park's very soft supply reflects the western San Gabriel Valley's Raymond Basin management. The Raymond Basin is one of the most actively managed groundwater basins in the Los Angeles metropolitan area — it is adjudicated (court-managed water rights) and managed by the Raymond Basin Management Board, with extensive MWD imported water spreading operations. The San Gabriel Valley Municipal Water District and Main San Gabriel Basin Watermaster coordinate spreading of soft MWD State Water Project imports (SWP hardness 20–50 mg/L) throughout the western San Gabriel Valley basin. The dominant SWP import fraction in the Raymond Basin recharge produces the very soft 49 mg/L at Monterey Park.

With hardness at 49 mg/L, Monterey Park residents enjoy very soft water with essentially no scale challenges. City of Monterey Park Public Works Water Division consistently delivers water meeting all California SWRCB and EPA Safe Drinking Water Act requirements.