Iowa ranks #2 of 37 in the DrainDispatch Drain Risk Index, with a composite score of 66 out of 100 — among the harder environments in the index. The median across all 37 states is 40.
What is driving the Iowa score
The larger of the two contributors in Iowa is freeze depth.
Freeze depth: 58 inches (sub-score 72/100)
The frost line in Iowa reaches roughly 58 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: 80-180 ppm (sub-score 43/100)
Supplies across Iowa typically test 80-180 ppm — slightly hard 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.
What this does and does not tell you
It describes an environment, not a property. A high score means buried drain lines in Iowa face more pressure on average. It says nothing about your house. Pipe material, the age of the lateral, how it was originally laid, and whether there are mature trees over it all matter at least as much — and none of them is in this version of the index.
Version 1.0 uses two factors. Housing age, tree canopy and storm intensity are planned for 2.0. We would rather publish two factors we can source than five we cannot.
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States either side of Iowa
Full index, all 37 states, with methodology →
Questions
What does a score of 66 mean for Iowa?
It places Iowa at #2 of 37 covered states for environmental pressure on buried drain lines — among the harder environments in 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 two normalised sub-scores: frost line depth (0 inches scores 0, 80 inches scores 100) and median municipal water hardness (20 ppm scores 0, 275 ppm scores 100). Iowa scores 72 and 43 respectively.
Why unweighted?
Because we have no defensible basis for preferring one factor over the other. 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?
Published state frost-line depth reference tables and published state water-hardness data. Both are cited on the methodology page.
Does a high score mean my Iowa drains will block?
No. It means the environment is harder on buried pipe on average. Housing age, pipe material and tree planting matter at least as much, and none of those is in version 1.0.