Rosario, WA
Lead detected, under the action levels
Latest 90th-percentile lead: 4.5 ppb (monitoring period 2022-2024). 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.
Who runs the water here
Rosario serves about 1,426 people through 367 service connections, which makes it a small system under EPA's size classes. It is privately owned and draws surface water, in San Juan County, Washington. EPA system ID: WA5374270. Ask the utility on your bill for your address in their service line inventory.
Every lead result on file
Against the period ending 2021 (3.7 ppb) the latest result is about the same. The highest 90th-percentile result EPA holds for Rosario is 4.5 ppb across 3 monitoring periods, none of them over 15 ppb.
| Period ending | 90th-percentile lead |
|---|---|
| 2024 | 4.5 ppb |
| 2021 | 3.7 ppb |
| 2018 | 3 ppb |
How Rosario compares
Of the 2,218 Washington systems with a lead result, the median latest reading is 1 ppb; 18 are over 15 ppb right now and 62 have gone over at some point. Rosario's 4.5 ppb sits at the 90th percentile in Washington and the 89th nationally (higher means more lead).
Other water systems in San Juan County
39 other systems share San Juan County; 9 of them have a higher latest lead result than Rosario. If you are unsure which one supplies your house, the name on your water bill decides it.
| System | People | Latest lead |
|---|---|---|
| Eastsound Water Users Association | 3,711 | 5.3 ppb |
| Friday Harbor Town Of | 3,543 | 1.6 ppb |
| Roche Harbor Water System Inc | 2,091 | 3.3 ppb |
| Fisherman Bay Water Association | 1,195 | 0 (not detected) |
| Doe Bay Water Users Assoc | 442 | 3.3 ppb |
| Olga Water Users Inc | 392 | 3.1 ppb |
| West Sound Water Association | 206 | 1.6 ppb |
| Cape San Juan Water District | 164 | 5.1 ppb |
| Oaks The Mobile Home Park | 143 | 1.1 ppb |
| Mackaye Harbor Water District | 133 | 1.5 ppb |
What to do in your house
Test your own tap with a certified lab first-draw sample; Eastsound, WA 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 Rosario 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. Why sampled homes are the worst-case ones is in the guide to reading the number. Systems that went over once often dip back under; here is what that means.