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Data report · 2026

Maryland Water Damage Risk Index

Where in Maryland is a house most likely to take on water? We combined Census housing age with ten years of daily weather for 23 of Maryland's 23 counties to rank them.

Highest index
Baltimore
Score 75 of 100
Most pipe-freeze nights
Garrett
42 nights ≤ 20°F a year
Oldest housing
Allegany
51% built before 1960
Most heavy-rain days
Baltimore
10.6 days ≥ 1 inch a year
< 4141–4747–5353–58≥ 58 index (0–100)

Key findings

  • The five highest-scoring counties are Baltimore, Dorchester, Allegany, Cecil, Washington. Each combines old housing with harsher-than-average winters or frequent downpours.
  • Allegany County has the oldest housing in the state, with 51% of homes built before 1960, against a county median of 20%.
  • Garrett County averaged 42 nights a year at 20°F or colder, the most of any county in the data. The county median is 12.
  • St. Mary's County has the newest housing, with 37% of homes built since 2000, which pulls its index down even where winters are cold.

Weather: NOAA nClimGrid-Daily county averages, 2015–2024. Housing: ACS 2020-2024.

All counties

Select a column header to sort.

Rank County Index Freeze nights Pre-1960 homes Heavy-rain days Muggy nights
1 Baltimore 75 17 32% 10.6 61
2 Dorchester 69 10 37% 9.7 81
3 Allegany 60 28 51% 6.5 21
4 Cecil 59 16 20% 9.6 68
5 Washington 58 22 34% 6.7 42
6 Talbot 57 10 26% 9.5 82
7 Prince George's 56 12 21% 9.5 76
8 Caroline 55 12 29% 9.3 69
9 Kent 55 13 32% 7.8 78
10 Harford 53 18 12% 9.5 64
11 Somerset 53 8 25% 9.5 90
12 Calvert 49 10 11% 10.2 83
13 Garrett 49 42 22% 5.6 5
14 Carroll 47 21 18% 9 44
15 Howard 47 17 6% 9.7 55
16 Anne Arundel 44 10 19% 9.3 84
17 Wicomico 44 10 21% 9.3 76
18 Montgomery 43 15 20% 8.4 62
19 Frederick 41 19 17% 8.3 49
20 Queen Anne's 37 12 13% 8.6 76
21 St. Mary's 37 9 10% 9.5 85
22 Charles 34 10 9% 9.4 83
23 Worcester 28 9 9% 9.1 85

Methodology

For each county with weather data, we convert four factors to a percentile rank among those counties (0 = lowest, 100 = highest), then take a weighted average:

  • Pipe-freeze nights (nights ≤ 20°F / yr), weight 30%
  • Homes built before 1960 (% of homes), weight 30%
  • Heavy-rain days (days ≥ 1 in / yr), weight 25%
  • Muggy nights (nights ≥ 65°F / yr), weight 15%

Freezing weather and old plumbing get the most weight because burst and failing supply lines are among the most common causes of household water damage. Heavy rain drives basement flooding and sewer backups, and warm, muggy nights mark the humid air that lets mold follow. The index is relative: a low score means lower risk than other Maryland counties, not no risk.

Limits: weather values are county-wide averages, so hollows, ridges and lakeshores can differ; ACS housing figures are survey estimates; the index doesn't account for floodplains, soil, or local sewer systems. Full details on our data sources page.

Cite this data

You're welcome to use these figures with attribution. Suggested citation:

Local Water & Mold, "Maryland Water Damage Risk Index 2026," https://localwatermold.com/maryland/maryland-water-damage-risk/. Data: U.S. Census Bureau ACS 2020-2024; NOAA nClimGrid-Daily 2015–2024.

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