Arizona ranks #20 of 37 in the DrainDispatch Drain Risk Index, with a composite score of 38 out of 100 — around the middle of the index. The median across all 37 states is 40.
What is driving the Arizona score
The largest of the three contributors in Arizona is water hardness.
Freeze depth: 10 inches (sub-score 12/100)
At roughly 10 inches, the Arizona frost line is shallow and frozen laterals are rare. That removes one of the two common causes of joint movement, which means recurring blockages here are more often about grade, grease or root pressure than about winter.
Water hardness: 200-350+ ppm (sub-score 100/100)
Municipal supplies across Arizona typically test 200-350+ ppm — hard to very hard. Hard water deposits scale on the inside of pipe over years. It rarely blocks a line by itself, but it narrows the effective diameter and gives grease and solids something to anchor on, which shortens the interval between blockages.
Housing age: median year built 1998 (sub-score 3/100)
Across the 51 Arizona towns we cover, the median home was built in 1998 (US Census ACS 5-year 2023, table B25035). Housing that new was almost certainly drained in PVC or ABS: smooth-walled, solvent-welded into long runs with far fewer joints. It does not scale and roots have much less to exploit, which is why newer stock scores low here even in states with hard water.
What this does and does not tell you
It describes an environment, not a property. A high score means buried drain lines in Arizona 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 51 Arizona 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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DrainDispatch routes drain and sewer calls to independent contractors across 55 Arizona towns and 250 ZIP codes. Coverage is not statewide. See every covered Arizona town →
States either side of Arizona
Full index, all 37 states, with methodology →
Questions
What does a score of 38 mean for Arizona?
It places Arizona at #20 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). Arizona scores 12, 100 and 3 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 51 Arizona towns we cover. All three are cited on the methodology page.
Does a high score mean my Arizona 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.