Mt Moonlight Basin, MT
Lead detected, under the action levels
Latest 90th-percentile lead: 0.28 ppb (monitoring period 2026-2026). 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.
Who runs the water here
Mt Moonlight Basin serves about 355 people through 408 service connections, which makes it a very small system under EPA's size classes. It is privately owned and draws groundwater, in Madison County, Montana. EPA system ID: MT0004023; phone on file: 406-580-1527. Call that number and ask whether your address has a lead, galvanized or unknown service line.
Every lead result on file
Against the period ending 2025 (0.22 ppb) the latest result is about the same. The highest 90th-percentile result EPA holds for Mt Moonlight Basin is 1.1 ppb across 10 monitoring periods, none of them over 15 ppb.
| Period ending | 90th-percentile lead |
|---|---|
| 2026 | 0.28 ppb |
| 2025 | 0.22 ppb |
| 2024 | 0 (not detected) |
| 2024 | 0.5 ppb |
| 2024 | 0 (not detected) |
| 2022 | 0.5 ppb |
| 2021 | 0 (not detected) |
| 2019 | 0 (not detected) |
| 2018 | 1.1 ppb |
| 2016 | 1.1 ppb |
How Mt Moonlight Basin compares
Of the 753 Montana systems with a lead result, the median latest reading is 1 ppb; 5 are over 15 ppb right now and 28 have gone over at some point. Mt Moonlight Basin's 0.28 ppb sits at the 40th percentile in Montana and the 41st nationally (higher means more lead).
Neighbouring systems
10 other systems share Madison County; 7 of them have a higher latest lead result than Mt Moonlight Basin. If you are unsure which one supplies your house, the name on your water bill decides it.
| System | People | Latest lead |
|---|---|---|
| Big Sky County Water And Sewer Dist 363 | 4,132 | 4.84 ppb |
| Virginia City Water Dept | 1,500 | 0 (not detected) |
| Ennis Town Of | 1,400 | 0 (not detected) |
| Sheridan Town Of | 632 | 2 ppb |
| Andesite Ridge Water System | 450 | 3 ppb |
| Twin Bridges Town Of | 424 | 2 ppb |
| Lower Pioneer Mountain Water System | 350 | 1 ppb |
| Valley Garden Golf Village Hoa | 195 | 1 ppb |
| Encampment Trail | 100 | 0 (not detected) |
| Lone View Ridge Water System | 37 | 1 ppb |
Your move
Test your own tap with a certified lab first-draw sample; Belgrade, MT 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 Mt Moonlight Basin 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. Size matters more than most people expect: small vs large water systems.