Washington County, Missouri · Potosi
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Washington County averages 30 nights a year at 20°F or colder, mostly November to February, and 21% of its homes predate 1960.
Basements flood here mostly in May. Washington County averages 12.7 days a year with an inch of rain or more.
Sewage backups in Washington County spike on heavy-rain days, about 12.7 a year, when sewer mains fill up and water finds the lowest drain.
Roof leaks here come from summer downpours and, with about 84 freeze-thaw days a year, from winter ice dams. Most show up as ceiling stains in the room below.
26% of occupied homes in Washington County heat mainly with wood or propane, close to the Missouri county median of 24.5%.
Muggy summer nights, lows of 65°F or more, come about 46 times a year in Washington County. Mold after a leak spreads fastest from June through August.
Local risk profile
Washington County covers 760 square miles of eastern Missouri, with about 23,470 residents and 10,734 homes. The county seat is Potosi, and Irondale, Mineral Point and Caledonia round out the largest towns. Much of its housing is recent, with a median build year of 1985.
50/100 Water Damage Risk Index: Elevated Washington County ranks 62 of 114 Missouri counties. See the statewide ranking and method.The three factors where Washington County ranks highest compared with other Missouri counties.
Pipe-freeze risk in Washington County sits near the middle of the state. In the 2015–2024 record the county logged about 30 nights a year at or below 20°F (44th of 114) and 97 below freezing. Twenty degrees is roughly where uninsulated pipes start to freeze.
The longest cold spell was straight 12 days without the temperature rising above freezing, ending in February 2021. The coldest night reached about -9°F on December 23, 2022. Burst pipes usually show up when a spell like that breaks and the ice thaws.
The freeze season here runs November to February, with January the coldest. If you travel then, leave the thermostat at 55°F or above and open sink cabinets on outside walls.
Freezing nights typically start around Oct 23 and end around Apr 15.
Heavy rain is a bigger factor here than in most of Missouri. The county gets about 50.1 inches of rain and melted snow a year, with 12.7 days of an inch or more (18th of 114). Those downpours cluster in April, May and August, when sump pumps and gutters are tested hardest. The wettest day on record brought 4.56 inches on November 5, 2024. The worst three-day stretch dropped 8.07 inches, ending November 6, 2024, the kind of soaking that overwhelms sump pumps and storm sewers.
Freeze-thaw days, below freezing overnight and above it by afternoon, come about 84 times a year here. They're the main driver of ice dams and of water working its way through foundation cracks in late winter.
Housing
43% of homes in Washington County predate 1980, below the Missouri county median of 53%, which ranks 92nd of Missouri's 114 counties.
The mix runs from 21% built before 1960 to 23% built since 2000, so older neighborhoods bring aging pipe while newer subdivisions bring failed appliance lines and water heaters.
34% date from 1980 to 1999, the window when polybutylene, a gray flexible plastic supply pipe, was used in some homes. It's prone to leaks at the fittings, so it's worth checking for in a house from those years.
Manufactured and mobile homes make up 28% of the housing here. Water lines in the underbelly depend on intact skirting and working heat tape, and they're usually the first to freeze in a cold snap.
Beyond water
Washington County averages 46 warm, muggy nights a year (lows of 65°F or more) and gets the most rain in May. The EPA recommends keeping indoor humidity below 60%, ideally 30 to 50%. Basements can pass 60% on their own in summer, so a dehumidifier matters even without a leak, and anything wet should be dried within 24 to 48 hours.
Mold remediation: what to expectBy main heating fuel, Washington County homes break down as 6% utility gas, 68% electric, 15% propane and 11% wood. Wood heat is above the Missouri norm. Annual chimney and vent inspection, which the NFPA recommends, is one of the most effective fire-prevention habits for these homes.
Fire and smoke cleanup: first stepsCoverage
Calls connect to restoration companies that work across Washington County. The largest communities by population:
Population from ACS 2020-2024 5-year estimates. Townships and unincorporated areas are covered too.
Nearby
Washington gets more pipe-freeze nights than any of its neighbors. It also has the most heavy-rain days in its area. Iron County has the oldest housing nearby, with 62% of homes built before 1980.
By the numbers
| Factor | Washington | Missouri median | Rank |
|---|---|---|---|
| Homes built before 1960 | 21% | 25% | 79 of 114 |
| Homes built before 1980 | 43% | 53% | 92 of 114 |
| Homes built 2000 or later | 23% | 21% | 48 of 114 |
| Manufactured or mobile homes | 28% | 9.8% | 2 of 114 |
| Vacant homes | 17% | 15% | 50 of 114 |
| Wood or propane heat | 26% | 25% | 59 of 114 |
| Nights at 20°F or colder | 30/yr | 28/yr | 44 of 114 |
| Days with 1 inch+ of rain | 13/yr | 10/yr | 18 of 114 |
| Freeze-thaw days | 84/yr | 77/yr | 25 of 114 |
| Muggy nights (65°F+) | 46/yr | 65/yr | 102 of 114 |
Rank 1 is the highest value. Bars run from the lowest to the highest Missouri county; the tick marks the median; orange means higher water damage risk than the median, green means lower.
Questions
Peak risk months in Washington County: freezing from November to February, heavy rain in April, May and August.
Sources: U.S. Census Bureau, ACS 2024 5-year estimates (2020-2024); weather from NOAA nClimGrid-Daily county averages (EpiNOAA), 2015–2024, averaged across the county; county boundaries from Census TIGER. Reviewed 2026-10-21. Methodology