National City Water Hardness & Quality Report (2026)

National City, California, in south San Diego County adjacent to Chula Vista and the Port of San Diego — the second-oldest city in San Diego County and a historically significant US Navy base community (home of the 32nd Street Naval Station) — draws its municipal water supply from the San Diego County Water Authority (SDCWA) and City of San Diego Water Utilities distribution via the City of National City Engineering Department Water Division. Water hardness in National City measures 164.5 mg/L — classified as hard.

National City's hard supply reflects the south San Diego County SDCWA distribution zone's Colorado River-dominated supply blend. South San Diego County communities (National City, Chula Vista, San Ysidro) are at the terminus of the SDCWA distribution system, furthest from the SWP Metropolitan Water District sources and receiving a higher proportion of the hard Colorado River Aqueduct supply (Colorado River at Lake Havasu: 300–600 mg/L raw hardness). The SDCWA south distribution zone carries higher Colorado River fraction than north county, producing harder water in National City (164.5 mg/L) compared to north coastal communities (Encinitas: 89.5 mg/L). Additionally, the south San Diego County distribution infrastructure is older vintage — the 1940s–1960s era of National City's naval and industrial expansion.

At 164.5 mg/L, National City residents face regular hard water challenges. Scale deposits form on faucet aerators, showerheads, and appliances within weeks — monthly descaling with citric acid solution is standard maintenance. City of National City and SDCWA consistently deliver water meeting all California SWRCB and EPA Safe Drinking Water Act requirements.