Gswc-San Dimas, CA
Lead detected, under the action levels
Latest 90th-percentile lead: 2.1 ppb (monitoring period 2024-2026). The federal action level is 15 ppb today and drops to 10 ppb in Nov 2027; EPA's health goal is 0. Lead was measured in sampled homes but the 90th percentile is under both action levels. EPA's health goal for lead is zero, so test your own tap if your home was built before 1986 or anyone in it is pregnant or a young child.
About Gswc-San Dimas
Gswc-San Dimas serves about 56,564 people through 16,184 service connections, which makes it a large system under EPA's size classes. It is privately owned and draws surface water, in Los Angeles County, California. EPA system ID: CA1910142; phone on file: 760-515-8322. They can tell you what your service line is made of and whether they pay to replace it.
Every lead result on file
Against the period ending 2026 (1.2 ppb) the latest result is about the same. The highest 90th-percentile result EPA holds for Gswc-San Dimas is 2.7 ppb across 6 monitoring periods, none of them over 15 ppb.
| Period ending | 90th-percentile lead |
|---|---|
| 2026 | 2.1 ppb |
| 2026 | 1.2 ppb |
| 2025 | 2.1 ppb |
| 2023 | 0 (not detected) |
| 2020 | 2.7 ppb |
| 2017 | 0 (not detected) |
Where this result ranks
Of the 2,884 California systems with a lead result, the median latest reading is 0 ppb; 30 are over 15 ppb right now and 215 have gone over at some point. Gswc-San Dimas's 2.1 ppb sits at the 79th percentile in California and the 74th nationally (higher means more lead).
Neighbouring systems
197 other systems share Los Angeles County; 15 of them have a higher latest lead result than Gswc-San Dimas. If you are unsure which one supplies your house, the name on your water bill decides it.
| System | People | Latest lead |
|---|---|---|
| Los Angeles-City, Dept. Of Water & Power | 3,875,566 | 3.9 ppb |
| Long Beach Utilities Department | 466,772 | 0.97 ppb |
| Santa Clarita Valley Water Agency | 292,014 | 0 (not detected) |
| Gswc - Southwest | 277,740 | 1.7 ppb |
| San Gabriel Valley Water Co.-El Monte | 240,000 | 0 (not detected) |
| Los Angeles Cwwd 40 Reg 4 & 34 Lancaster | 208,129 | 1.8 ppb |
| Glendale-City, Water Dept. | 192,212 | 5.3 ppb |
| Suburban Water Systems-San Jose | 170,523 | 0 (not detected) |
| Pasadena Water And Power | 165,448 | 1.9 ppb |
| Pomona - City, Water Dept. | 151,713 | 2.1 ppb |
What to do in your house
Test your own tap with a certified lab first-draw sample; San Dimas, CA may offer free or low-cost kits through the utility. If your own line is lead, replacing the private side runs about $1,200-$12,300 (EPA average about $4,700). Ask Gswc-San Dimas whether it covers that cost before hiring anyone - many utilities now do.
These figures describe homes the utility sampled, not your tap. Only your service line record or a test of your own water answers the question for your house. The lead result guide covers how utilities pick the homes they sample. The action level is dropping - the 10 ppb rule from 2027.