Rainbow Lake, WA
Lead detected, under the action levels
Latest 90th-percentile lead: 5 ppb (monitoring period 2023-2025). 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.
About Rainbow Lake
Rainbow Lake serves about 168 people through 67 service connections, which makes it a very small system under EPA's size classes. It is owned by a local government (city, town, county or district) and draws groundwater, in Mason County, Washington. EPA system ID: WA5370791. Ask the utility on your bill for your address in their service line inventory.
Lead results over time
Against the period ending 2022 (5.8 ppb) the latest result is about the same. The highest 90th-percentile result EPA holds for Rainbow Lake is 5.8 ppb across 4 monitoring periods, none of them over 15 ppb.
| Period ending | 90th-percentile lead |
|---|---|
| 2025 | 5 ppb |
| 2022 | 5.8 ppb |
| 2019 | 1 ppb |
| 2016 | 2 ppb |
How Rainbow Lake 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. Rainbow Lake's 5 ppb sits at the 91st percentile in Washington and the 91st nationally (higher means more lead).
Neighbouring systems
119 other systems share Mason County; 8 of them have a higher latest lead result than Rainbow Lake. If you are unsure which one supplies your house, the name on your water bill decides it.
| System | People | Latest lead |
|---|---|---|
| Shelton City Of | 15,273 | 1.8 ppb |
| Belfair Water District 1 | 4,432 | 0 (not detected) |
| Lake Cushman System 5 | 3,675 | 2 ppb |
| Timberlake Community Club Inc | 2,337 | 5 ppb |
| Washington Corrections Center | 2,223 | 1.6 ppb |
| Alderbrook Water Co | 2,154 | 0 (not detected) |
| Lake Limerick Water | 2,148 | 0 (not detected) |
| Lakeland Village Water | 2,120 | 0 (not detected) |
| Hoodsport | 1,853 | 2 ppb |
| Shorecrest Estates Water Co | 1,321 | 1 ppb |
What to do in your house
Test your own tap with a certified lab first-draw sample; Shelton, 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 Rainbow Lake 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.