Three things measurably shape how often a drain line gives trouble, and all three vary enormously by state: how deep the ground freezes, which drives the joint movement that lets roots in; how hard the water is, which drives the scale that narrows a pipe over decades; and how old the housing is, which is the best available proxy for what the buried pipe is actually made of.

We combined published figures for all three into a single 0–100 score across the 37 states where we have coverage and all three data points. Higher means more pressure on buried drain and sewer lines.

Read the limitations before citing this. This is a state-level index built from state-level figures, so it cannot tell you about your street — it compares environments, it does not predict any individual property. It does not include tree canopy or storm intensity, both of which matter. The housing-age component is a median of medians: we take the US Census median year built for each town we cover and take the median across the state. 5 states are marked † because fewer than 20 of their towns had housing data, and a median from a small sample should be read with caution.

The index

#	State	Composite	Frost	Frost score	Hardness	Hardness score	Median year built	Age score	Towns
1	Minnesota	67	80″	100	150-300 ppm	80	1988	20	62
2	Iowa	66	58″	72	80-180 ppm	43	1950	83	48
3	Indiana	64	36″	45	150-350 ppm	90	1966	57	183
4	New York	49	50″	62	30-120 ppm	22	1963	62	391
5	Utah	48	30″	38	200-350+ ppm	100	1996	7	50
6	Maine †	48	74″	92	20-100 ppm	16	1979	35	12
7	Kansas †	48	32″	40	150-350+ ppm	90	1992	13	9
8	Pennsylvania	46	44″	55	60-180 ppm	39	1973	45	368
9	Missouri	46	33″	41	100-300+ ppm	71	1985	25	103
10	Colorado	46	44″	55	120-250 ppm	65	1989	18	107
11	New Mexico †	45	18″	22	150-350+ ppm	90	1987	22	5
12	New Jersey	44	36″	45	50-150 ppm	31	1966	57	473
13	Ohio	43	32″	40	80-180 ppm	43	1972	47	187
14	Illinois	43	36″	45	60-180 ppm	39	1973	45	245
15	New Hampshire	42	60″	75	20-100 ppm	16	1979	35	132
16	California	42	5″	6	100-300 ppm	71	1971	48	263
17	Rhode Island	40	38″	48	30-120 ppm	22	1970	50	46
18	Oklahoma	40	20″	25	120-300 ppm	75	1988	20	40
19	Massachusetts	40	32″	40	30-120 ppm	22	1966	57	178
20	Arizona	38	10″	12	200-350+ ppm	100	1998	3	51
21	Texas	36	10″	12	150-350+ ppm	90	1997	5	132
22	Maryland	36	30″	38	60-180 ppm	39	1981	32	176
23	Idaho	34	31″	39	20-180 ppm	31	1981	32	31
24	West Virginia †	32	32″	40	80-180 ppm	43	1992	13	4
25	Delaware	31	32″	40	60-180 ppm	39	1992	13	49
26	Kentucky	30	15″	19	100-180 ppm	47	1985	25	404
27	Florida	30	0″	0	100-300 ppm	71	1988	20	150
28	Virginia	29	18″	22	60-180 ppm	39	1984	27	119
29	Louisiana	26	4″	5	100-180 ppm	47	1984	27	45
30	North Carolina	25	10″	12	60-180 ppm	39	1986	23	204
31	Tennessee	24	12″	15	80-180 ppm	43	1991	15	114
32	Oregon	24	18″	22	20-120 ppm	20	1982	30	114
33	Washington	23	24″	30	20-120 ppm	20	1989	18	74
34	South Carolina	22	4″	5	80-180 ppm	43	1990	17	81
35	Georgia	20	5″	6	80-180 ppm	43	1993	12	119
36	Hawaii	18	0″	0	20-100 ppm	16	1978	37	31
37	Mississippi †	17	8″	10	80-150 ppm	37	1997	5	16

Methodology

Frost depth is the published state frost-line figure in inches, normalized linearly from 0″ (score 0) to 80″ (score 100).
Water hardness is the midpoint of the published state hardness range in ppm, normalized linearly from 20 ppm (score 0) to 275 ppm (score 100).
Housing age is the median across the towns we cover of the US Census median year structure built (ACS 5-year 2023, table B25035), normalized so that a median of 1940 scores 100 and 2000 scores 0. Older housing scores higher because it is more likely to sit on jointed clay or cast-iron laterals rather than plastic.
Composite is an unweighted mean of the three sub-scores. We chose equal weighting because we have no defensible basis for preferring one over another — and we would rather say that than invent a weighting that looks more scientific than it is.
States missing any of the three are excluded rather than estimated. In practice that is one state. We cover 38; the index ranks 37. Arkansas is excluded because we have no water-hardness figure for it. We would rather leave a gap than fill it with an estimate and then rank a state on our own guess — and if you are wondering why the count here differs from the coverage figure elsewhere on the site, that is why.

What the third factor changed

Adding housing age moved the table substantially, and in a direction worth understanding. Iowa rises sharply on a median build year of 1950 — the oldest housing stock in our coverage — despite unremarkable water. New York and New Jersey rise for the same reason. Arizona and Texas fall: the water is genuinely hard, but the housing is new enough that most of it is on plastic pipe that does not care. That is the point of including it. Hard water attacking a PVC lateral laid in 1998 is a much smaller problem than soft water around jointed clay laid in 1935.

How to read it, and how not to

A high score means the environment and the likely pipe are harder on a buried line, not that your drain will block. Tree planting, how the line was originally laid and bedded, and what has gone down it since all matter, and none of them is in here.

Download the data

The full index is available as a CSV: drain-risk-index-v1.csv — rank, state, composite, frost depth, water hardness, median year built and all three sub-scores. Published under CC BY 4.0, so you may republish or adapt it, including commercially, with attribution.

Every state also has its own page with the numbers behind its ranking. Click any state in the table above.

License and reuse

This index is published under Creative Commons Attribution 4.0. You are free to use, adapt and republish it, including commercially, with attribution to DrainDispatch. If you use it, we would appreciate a link back, though the license requires attribution rather than a link specifically.

How to cite this index

The index is archived with Zenodo, operated by CERN, under a permanent DOI. Cite the DOI rather than this page — it will keep resolving whatever happens to this website.

DrainDispatch (2026). Drain Risk Index v1.0: state-level environmental pressure on residential drain and sewer lines in the United States [Data set]. DrainDispatch. https://doi.org/10.5281/zenodo.21908104
That DOI (10.5281/zenodo.21908104) always resolves to the current version. To pin this exact release instead, cite 10.5281/zenodo.21908105.

Sources and their limits. Housing age is US Census Bureau, American Community Survey 5-year estimates 2023, table B25035 — a primary source. The other two are weaker and we would rather say so: frost depth and water hardness are compiled state-level figures from published secondary sources, and neither quantity is genuinely a per-state constant. Frost depth is set by local building jurisdictions (IRC Table R301.2(1)); water hardness is a property of each individual supply, and the USGS national mapping is regional and historical. Each source and its scope is set out on the methodology page. If you are citing this index, cite those limits with it.

The Drain Risk Index — Where America’s Drains Work Hardest