Lyon-Sioux Rws-Big Sioux, IA
Lead detected, under the action levels
Latest 90th-percentile lead: 4 ppb (monitoring period 2025-2025). 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
Lyon-Sioux Rws-Big Sioux serves about 1,530 people through 612 service connections, which makes it a small system under EPA's size classes. It is privately owned and draws groundwater, in Lyon County, Iowa. EPA system ID: IA6000755; phone on file: 712-472-3755. Ask them for your address in their service line inventory - every system had to publish one by Oct 2024.
Lyon-Sioux Rws-Big Sioux's lead record
Against the period ending 2025 (3.3 ppb) the latest result is about the same. The highest 90th-percentile result EPA holds for Lyon-Sioux Rws-Big Sioux is 6.3 ppb across 5 monitoring periods, none of them over 15 ppb.
| Period ending | 90th-percentile lead |
|---|---|
| 2025 | 4 ppb |
| 2025 | 3.3 ppb |
| 2022 | 3.9 ppb |
| 2019 | 5.8 ppb |
| 2016 | 6.3 ppb |
Where this result ranks
Of the 1,066 Iowa systems with a lead result, the median latest reading is 1.4 ppb; 4 are over 15 ppb right now and 36 have gone over at some point. Lyon-Sioux Rws-Big Sioux's 4 ppb sits at the 84th percentile in Iowa and the 88th nationally (higher means more lead).
Neighbouring systems
11 other systems share Lyon County; 2 of them have a higher latest lead result than Lyon-Sioux Rws-Big Sioux. If you are unsure which one supplies your house, the name on your water bill decides it.
| System | People | Latest lead |
|---|---|---|
| Rock Rapids Municipal Water Works | 2,611 | 1.5 ppb |
| Lyon-Sioux Rws-Doon | 1,765 | 4 ppb |
| Lyon-Sioux Rws-Rock Rapids | 1,187 | 2 ppb |
| George Water Supply | 1,082 | 2 ppb |
| Inwood Water Supply | 928 | 2.1 ppb |
| Larchwood Water Supply | 926 | 2.4 ppb |
| Doon Water Supply | 619 | 4 ppb |
| Lyon-Sioux Rws-Boyden | 605 | 5.3 ppb |
| Little Rock Water Supply | 441 | 9.1 ppb |
| Lester Water Supply | 296 | 2.2 ppb |
Next steps for Rock Rapids, IA
Test your own tap with a certified lab first-draw sample; Rock Rapids, IA 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 Lyon-Sioux Rws-Big Sioux 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. What a 90th-percentile result does and does not tell you: how to read a lead result. Size matters more than most people expect: small vs large water systems.