New Hampshire ranks #15 of 37 in the DrainDispatch Drain Risk Index, with a composite score of 42 out of 100 — around the middle of the index. The median across all 37 states is 40.
What is driving the New Hampshire score
The largest of the three contributors in New Hampshire is freeze depth.
Freeze depth: 60 inches (sub-score 75/100)
The frost line in New Hampshire reaches roughly 60 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: 20-100 ppm (sub-score 16/100)
Supplies across New Hampshire typically test 20-100 ppm — soft to moderately 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 1979 (sub-score 35/100)
Across the 132 New Hampshire towns we cover, the median home was built in 1979 (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 New Hampshire 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 132 New Hampshire 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.
Need a drain cleared in New Hampshire?
We route calls across 143 New Hampshire towns and 167 ZIP codes.
Call (888) 855-8790Drain cleaning coverage in New Hampshire
DrainDispatch routes drain and sewer calls to independent contractors across 143 New Hampshire towns and 167 ZIP codes. Coverage is not statewide. See every covered New Hampshire town →
States either side of New Hampshire
Full index, all 37 states, with methodology →
Questions
What does a score of 42 mean for New Hampshire?
It places New Hampshire at #15 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). New Hampshire scores 75, 16 and 35 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 132 New Hampshire towns we cover. All three are cited on the methodology page.
Does a high score mean my New Hampshire 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.