Maryland ranks #21 of 37 in the DrainDispatch Drain Risk Index, with a composite score of 36 out of 100 — around the middle of the index. The median across all 37 states is 40.
What is driving the Maryland score
The largest of the three contributors in Maryland is water hardness.
Freeze depth: 30 inches (sub-score 38/100)
The frost line in Maryland reaches roughly 30 inches, which is deep. Waste lines, yard drains and downspout runs set shallower than that can freeze outright, but the more consequential effect is slower: repeated freeze and thaw shifts buried pipe and opens joints. Open joints are where tree roots get in, which is why deep-frost states tend to see root intrusion as a recurring rather than a one-off problem.
Water hardness: 60-180 ppm (sub-score 39/100)
Supplies across Maryland typically test 60-180 ppm — soft to hard. Softer water means slower scale build-up, so the effective diameter of a sound pipe holds up better over decades than it does in hard-water states.
Housing age: median year built 1981 (sub-score 32/100)
Across the 176 Maryland towns we cover, the median home was built in 1981 (US Census ACS 5-year 2023, table B25035). That straddles the change-over from cast iron and clay to plastic. A house from this period can have either, and it is common to find a plastic replacement indoors still running out to an original clay lateral — which means the weakest section is usually the one nobody has looked at.
What this does and does not tell you
It describes an environment, not a property. A high score means buried drain lines in Maryland face more pressure on average. It says nothing about your house. Your own pipe material, how the lateral was originally laid and whether there are mature trees over it all matter at least as much — and none of those is in the index, because none of them can be sourced state by state.
Housing age here is a state median, not your house. It is the median across the 176 Maryland towns we cover, so it is a reasonable proxy for the pipe most homes in the state were built with and a poor one for any single address. A 1961 house on this street may have been repiped in 2015.
Version 1.0 uses three factors. Tree canopy and storm intensity are planned for 2.0. We would rather publish three factors we can source than five we cannot.
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States either side of Maryland
Full index, all 37 states, with methodology →
Questions
What does a score of 36 mean for Maryland?
It places Maryland at #21 of 37 covered states for environmental pressure on buried drain lines — around the middle of the index. It is a relative measure across states, not a prediction for any individual property.
How is the score calculated?
An unweighted mean of three normalized sub-scores: frost line depth (0 inches scores 0, 80 inches scores 100), median municipal water hardness (20 ppm scores 0, 275 ppm scores 100), and housing age from the US Census median year structure built (a median of 2000 scores 0, 1940 scores 100). Maryland scores 38, 39 and 32 respectively.
Why unweighted?
Because we have no defensible basis for preferring one factor over another. We would rather say that than invent a weighting that looks more scientific than it is.
Can I republish this?
Yes. The index is published under Creative Commons Attribution 4.0, so you are free to use, adapt and republish it, including commercially, with attribution to DrainDispatch.
Where does the data come from?
Three published sources: state frost-line depth reference tables, state water-hardness data, and US Census ACS 5-year 2023 table B25035 for median year structure built, aggregated across the 176 Maryland towns we cover. All three are cited on the methodology page.
Does a high score mean my Maryland drains will block?
No. It means the environment is harder on buried pipe on average. Your own pipe material, how the lateral was laid and whether there are mature trees over it matter at least as much, and none of those can be sourced state by state, so none is in version 1.0.